Pixar and Disney's collaboration over the years has brought us a number of unforgettable animated movies and has proven to be a major influence in the film industry. Those movies left a mark in each and every one of us and we still carry them with us to this day. I can't even begin to tell you how many expressions came from those movies. I am so glad most people understand what I'm referencing, that would make communicating a lot harder if they didn't.

While Disney movies tend to target mostly a young public, Pixar is known to create movies that attract children and adults alike. One of the main reasons those movies are loved by adults just as much as children is the amount of jokes hidden them (and, of course, the hidden ones too). These references throughout the movies constantly grab out attention back to reminisce to some childhood memories, bringing us back to carefree days.

Monsters Inc. is on the list of Pixar movies that marked my younger years. I have watched this movie many times over the years and am amazed every time at how well made and incredibly complex this supposed children's movie is. Monsters Inc. is one of those movies that has a ton of hidden gems. Some are in plain sight and one can easily spot them, some others are more hidden and you need to really pay attention to catch but a glimpse of them gems and some are you would never even have guessed were there. Come along with me in a trip down memory lane and let us revisit one of Pixar's classic through a collection of things we never knew existed.

Let's try to see how many you knew about already, shall we?

25 A Collection Of Easter Eggs

One thing the Pixar movies creators are good at is hiding Easter Eggs in plain sight. If you watch closely, you'll find hidden references to other Pixar movies, or real-life people and places lurking in a lot of their movies. Unsurprisingly, Monsters Inc. is no exception. There are quite a few Easter Eggs hidden in this movie, so be prepared. I hope you're ready for your world to change from all the things you've missed in this movie!

We find our first one in Boo's room, where you'll see a little plane on the left side of the shelf.

That's right, that's the toy plane that Buzz used to fly with in the Toy Story movie! There are a lot of Toy Story references in Monsters Inc. For this and many good reasons, Toy Story is one of the best movies out there.

24 Haven't I Seen That Place Before?

I've always thought that this trailer looked oddly familiar but I was never able to pinpoint where I'd seen it before. In case you haven't recognized it yet, let me give you a hint in the form of a very bad pun, on the off chance you haven't had enough of those in your life lately:

This has been bugging me for years, and I can't stop thinking about it.

Get it? No? I'm just gonna tell you: it's the same trailer seen in A Bug's Life (get it, "bugging me"? A Bug's Life? Ok, I'm out). It's the one Tilt goes to in search of mercenaries. I can't believe it took me so long to realize that — what's even weirder is the Pizza Planet truck from Toy Story parked right next to the trailer. Everything is connected.

23 Playing It Safe

We all remember that adorable scene where Boo sings in the bathroom. We probably all replayed the scene many times to understand what she was singing, but never managed to grasp a word she said.

That actually makes sense because it turns out that whatever Boo is singling is literally just gibberish.

As the actress who gave her voice to Boo, Mary Gibbs said in an interview that the creators asked her to sing for this scene. She chose "The Wheels On The Bus," but they didn't want to have any copyright issues so they asked her make up words. She sang for a little while and the creators ended up picking the parts they liked best to use in the movie.

22 Not So Blended

There's one scene I've always liked in this movie, and it was Randall's pre-scaring warm-up. In order to get his head into the game, he blends into a few different backgrounds before heading to his door, and this is precisely where our next Monsters Inc secret is hidden!

One of those backgrounds is a sky blue wallpaper with clouds. It so happens to be the exact wallpaper in Andy's room, in Toy Story.

There's a number of little Easter Eggs hidden throughout the movie but most of them are a bit more subtle than this one. The creators must have had so much fun adding all those elements from previous movies into Monsters Inc, and we can tell the whole process was just too much fun.

21  What On Earth Is That?

I'm not even sure I want to get into this because of how gross it is... but, it has to be done. It is expected that Monsters have a different food regime than we humans do, but there is one thing in this movie that I simply cannot get over. What is the deal with their "coffee"?

To each their own choice, but this might be a bit too much...

I put "coffee" in quotes because it seems that they don't drink coffee, per se, but actually something brownish that's been heated up. You can see it in the picture above, it very much seems that Mr Waternoose is pouring himself a large fuming cup.

I don't know, maybe it's just me but what else could that be, really? Hot mud?

20 A Collection Of Easter Eggs, Take 2

If you look really carefully at the bottom right corner, there's a doll on the floor. It happens to be Jessie, the female cowboy (cowgirl?) from Toy Story 2. You can also see the ball on the left, that's also from Toy's Story.

It actually lends lots of credence to the popular fan theory that all Pixar movies are in fact related, and that the toys had a history before they arrived in Andy's possession.

Reusing some small toys and random places that have been seen before would be easy to miss, but including an actual character from another movie is honestly brilliant. If that fan theory is to be believed, it may be possible that Jessie was in someone else's hands before she got to Andy's mom. I don't know about you, but I would love for that to be true.

19 Code 2319

Ever wondered what the code 2319 stood for? Yeah, me too. But, as it turns out, this code isn't really as ominous as it may seem, though it wasn't overtly explained in the film.

I've always thought it was random numbers put together, but when you think of it, it obviously had to mean something specific.

In every workplace, there are codes that one uses to alert others of a certain event that just occurred. In the movie, a code 2319 refers to the white sock stuck on George's back. Let me explain; if you put the two numbers 23 and 19 in relation to the alphabet, 23 = W and 19 = S so that's WS --> White Sock.

I know, that's totally weird!

18 Welcome To The Staff Party!

Here's another hidden gem for you: all the names on the Scare board actually belong to Pixar staff. This is another instance of those hidden things no one would know about, if it wasn't for people who research everything about movies, which is encouraging! There's always more to look for, hidden right under our noses.

This was a great inside joke for the Monsters Inc staff and crew!

It's one of those things that doesn't change anything about the movie for us, but it's such a nice way to thank the people who worked so hard and for so long to create the movie. These kinds of hidden info always warm my heart, because you can totally feel the camaraderie in the film staff and crew.

17 Boo's Real Name?

For some reason I never questioned the fact that Boo's name wasn't just "Boo" as a child, until I noticed that there was a name handwritten on one of Boo's drawings. This doesn't make any changes to the story itself, but it totally changes how we picture Boo as a grown character, or even just as herself.

Can we just keep calling her "Boo"? We don't like change.

The moment passes very quickly, but if you look closely at the bottom right hand of the screen when Boo is about to show Sully her drawing of Randall, you can see that the drawing on top has the name "Mary" written on it. Mary is actually the name of the actress who gave her voice to our little sweet kid, which is a cute nod to the cast as well!

16 Coincidence? I Think Not!

Ok, so we've known for some time now that Pixar loves to have their characters make cameos in movies that aren't their original design. Pixar also loves to foreshadow future movies, as we will see.

Tumblr user Ranting Randall came up with a theory that sent shivers down my spine. However, the passage mentioned to prove their point doesn't exist in the movie, but we can still ask ourselves if the theory could be true regardless.

In one of Toy's Story short "Partysaurus Rex," we can see a toilet cover that strangely looks like Sully's fur. Would Pixar dare imply that Sully's fur was... repurposed? And could that be the reason why we only got a prequel to Monsters Inc, and not a sequel?

I don't like what I see here. No, sir.

15 A Collection Of Easter Eggs, Take 3

Is that just me or does that orange fish look oddly familiar? Wait, isn't that our favourite clown fish? Why, yes! It's Nemo, of Finding Nemo fame!

Among the handful of toys Boo gives Sully at the end of the movie is a little orange fish, and that definitely is Nemo. The last time we saw them, they were looking to find their friend in Finding Dory. We wonder if the world of Monsters Inc has heard of any escaped fish, singing whales or cute otter hold-ups on freeways.

So we have yet another character from a previous movie that makes a little cameo! Nemo actually gets two cameos in the movie: he appears in toy form in Boo's bedroom and in paint form on one of the restaurant's walls.

14 Monster Revealed

If your mind hasn't be blown away by the meaning of the code 2319 just yet, allow me to put an suggestion in your mind that you will never be able to get rid of. I doubt anyone ever questioned the fact that the Monsters in Monsters Inc. don't wear clothes, for the most part.

But think about this: during the process of decontamination, George is completely cleaned by the CDA squad. The curtain drops and George suddenly realize that he has no clothes on at all! Yup, ladies and gentlemen, that's a revealed Monster!

So now the question is... why do some Monsters wear clothes, while others don't? If they all go bonkers over a child's sock entering their world, why would they be wearing human clothes?

I smell something fishy here...

13 What Is The Meaning Of This?

I realize now that there's a lot of things I never noticed in Monsters Inc. One of those more subtle ones has to be the name of the restaurant Mike and Celia go too: HarryHausen's. The restaurant is actually named after Ray Harryhausen, a stop-motion animator who worked on countless animated works.

I really enjoy the references made to the people who worked on the film, it must be super rewarding to see that on a project you've invested so many hours into.

Again, it's one of those things that most people wouldn't get, and that's what's most beautiful about it. The creators named the restaurant after a pioneer of stop-motion animation as a tribute to his life's work, which is really awesome.

12 That's One Comfy Armchair

One of my silly goals in life is to find the perfect armchair to put in my library. I want the prettiest, comfiest chair possible. Sully's chair seems to have all the criteria that make a perfect chair, but there's something a little off...

Have you ever noticed the hole at the back of Sully's chair?

One could wonder why on Earth would there be a hole at the back of an armchair. Well, let me shed some light on that: Sully has a tail! I con only imagine how uncomfortable sitting on one's tail must be, so in order to sit comfortably in his chair, Sully had a hole added to the back to let his tail hang out and not crush it under his weight.

That's one smart Monster.

11 What Have I Done?

This scene always made me laugh, both because of Sully's faces and repeated fainting, but also because we, as viewers, know that his panic is totally unjustified. But it doesn't make the hilarity of the scene any less memorable. I mean, just look at that face!

What I didn't know is that this scene is actually based on a Looney Tunes short entitled "Feed the Kitty."

The short shows a dog adopting a small kitten and attempting to keep it hidden, as he goes through roller coasters of emotion. We see the parallel! I don't know about you, but I've stopped counting the references to other movies in Monsters Inc., this movie is just one giant tribute to animated movies. That's totally awesome!

10 The Return Of The Tea Party Queen

Talking about references to other movies, I'm sure you won't be surprised if I tell you there's yet another reference to Toy Story. The creators were very proud of their other movie, that's for sure.

The teacher who gives a tour of the company to Boo and a small group of kids is called Mrs Nesbitt!

This is in reference to Buzz's alter ego in Toy Story. If it sounds a bit obscure to you, let me refresh your memory: after losing some parts, Buzz is adopted by Sid's sister. She dresses Buzz up and has him host a tea party for the other toys that Sid broke. At this point, Buzz feels rather poorly, and when Woody comes to save him, he tells him that he now is Mrs Nesbitt. He validates this information by pointing to his hat.

It seems that the clothes do make the man, sometimes.

9 From Child To Toddler

Boo is one of those adorable characters that we simply can't imagine any differently. But she wasn't always supposed to be so young and cute. We're never gonna get over her sweet little faces and cute gurgly noises, though.

Indeed, in some of the early versions of the movie, Boo was actually supposed to be around 6 years-old instead of being a toddler.

Her being older would certainly have made the story a little different, and maybe even funnier. The reason why the creators decided to make Boo a toddler was mainly to make her more dependent on Sully, and therefore create a deeper connection between the two characters. We totally get that creative choice!

8 You Shall Be Promoted

While we're on the subject of early versions and things that never were, it was revealed by the creators that Sully wasn't always the n°1 Monster on the block, and also that Mike wasn't always his companion.

Actually, Mike was never supposed to exist at all, in the early plans for the movie.

Hard to imagine those two separately, right? Well, when the creators first started to make plans for the story, they had Sully be a janitor who just stumbled across a door and found a human child. Along the same plot, Mike wasn't suppose to exist at all. How weird is that? I personally am glad they changed that because I just love the Sully/Mike duo.

7 Mike's New Car

Fun fact: a short was included in the Monsters Inc. DVD in 2002, and it starred Mike and Sully. The short is entitled "Mike's New Car" and shows the two characters testing out, well, Mike's new vehicle.

One of the things you need to know about this short is that it actually was the first Pixar short to use dialogues as well as the first to feature characters from a previous movie.

The scene was also supposed to be included in the movie but ended up being cut during the montage so the creators simply added it as bonus content in the DVD. It's really cool to see Pixar continue to test the waters of animation like this, it's really what keeps them on top in a world of fierce competition.

6 A Game Of Charades, Harry?

I am a massive fan of Harry Potter so this fact made me super happy. Both Harry Potter and the Philosopher's Stone and Monsters Inc were released the same year in 2001 (feeling old yet?) and the creators of Monsters Inc. pulled out all the stops.

They made a special trailer for their own movie to show before the screening of Harry Potter and the Philosopher's Stone.

In this trailer, we can see Mike and Sully playing a game of charades. Sully is trying to have Mike guess the name of a character that so happens to be Harry Potter. As you can guess, Mike isn't the most clever Monster out there so the whole thing turns out to be quite the challenge. I could describe the scene to you but it honestly wouldn't do it justice.

You have to see it, because it is just hilarious!