The Metal Gear series is the most well-known creation by video game designer, screenwriter, director, and producer Hideo Kojima. It is an action-adventure stealth game which was first released in 1987 on the original NES. You usually take on a character who's code-name is some variation of Snake. In Metal Gear Solid 2 and Metal Gear Rising: Revengeance, you take control of the former child soldier Raiden.

Players take on the game in different ways, such as speed-running it to get straight to the ending and onto their next adventure or maybe they're more like you. They are fans of the Metal Gear series and want to comb through every inch of the snowy landscapes or hot desserts to uncover something new. Hidden secrets, metaphors, and plot-twists are now known to be a huge part of the series. Many of the secrets are random Codec calls or silly hats. Some secrets are call-backs to Kojima's other creative masterpieces, such as Playable Trailer or P.T., which was planned to become Silent Hills.

This list will contain spoilers, so only scroll down if you're ready to delve deep into the series. There's more than enough hidden secrets within the Metal Gear series to shock even the most devoted fan. No matter what kind of player you are, you're sure to miss some shocking secret messages.

15 Demons Cannot Hide Their Bloodthirsty Ways

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Metal Gear Solid V: The Phantom Pain holds a hidden mechanic. If you butcher everyone and everything in your path, you will accrue Demon Points. These points are a test of Venom Snake's (and your) morality points. The more Demon Points you have, the larger the horn Venom Snake will grow. Your first horn will start sprouting at 20,000 points, where the metal shard in Venom Snake's head starts to grow, much like Pinocchio's nose.

Continue your ruthless killing streak to 50,000 points and the shard in Venom Snake's (or now Horned Snake) head will grow longer. The blood you shed will remain on your body as a permanent reminder that you have become a demon.

If you suddenly change your bloodthirsty ways, Demon Points can also be removed. Gain enough Heroism points and your Demon ways can be reversed. Want to prove you and Venom Snake are good guys? You'll have to prove it with your actions.

14 Silent Hills are Still Among Us

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Playable Trailer, or P.T., and the Metal Gear series are just a few of Kojima's creations. P.T. was a playable trailer for Silent Hills. It was meant to be be a new addition to the Silent Hill series and star The Walking Dead star Normal Reedus. Unfortunately, P.T. was canceled by Konami, scrubbed from the PlayStation Network, and Kojima eventually left the company.

P.T. has not met its death and lives on within Metal Gear Solid V: The Phantom Pain. Several references are hidden within this game, but are easy to miss. In mission 20 within the Ngumba Industrial Zone, pay attention to the boomboxes. You'll hear a variety of news stories revolving a series of murders. One of those murders includes Lisa Garland, who was a character planned for Silent Hills.

In addition to news, music from P.T. can be found on a cassette tape. Ludvig Forssell, who worked on the soundtrack for Metal Gear Solid V, also composed the music featured in P.T. News stories, music, and character references reveals that Kojima wants fans to remember the series that never came to light.

13 You're Not Ocelot Revolver's First Victim

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The torture device in Metal Gear Solid has caused many player restarts. Ocelot Revolver uses this device on Solid Snake to learn more about operating REX. Not only does Snake have to endure physical pain, but he's also threatened that Meryl Silverburgh would be killed if he didn't cooperate. Ocelot may not truly intend to kill Snake, but he wants to make him so uncomfortable that he would rather reveal REX's secret than to endure the pain.

Though Snake is tough, if you're not careful, it can be easy for Solid Snake to be electrocuted to death during this sequence. It may be intentional or an accident. After Snake's death, Liquid Snake will get upset at Ocelot. Not because he cares that Solid Snake is dead, but because this is not the first person Ocelot has killed. You'll learn that this device was also used to kill DARPA Chief Donald Anderson.

12 Invincible Ninja Cats Exist

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In Metal Gear Rising: Revengeance, there is a ninja cat you can find wandering around. A white cat is located towards the beginning of the game on the beach in R-01. This is the same cat found in the original Revengeance demo. This cat must have seen a lot of action because it is not afraid of Raiden or his sword.

If for some reason you feel that this cat needs to die by Raiden's hand, you can attack it. But don't expect to actually defeat it. When you attack the cat, he will evade every attack. You can try your hardest, but the cat cannot die. The cat will elegantly backflip or move out of the way. The cat can also be seen during a cutscene before fighting the cybernetic ninja Monsoon. Move around the camera and you'll spot a guard stop to pet a stray white cat. This may be a different cat, but its fearlessness is obvious.

11 You Need to Save Your Game. Now.

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The first Metal Gear Solid game was released during an era where auto-save didn't exist and memory cards were essential. If you forgot to save because you believed you could handle a difficult area and ended up getting slaughtered, you would have to replay hours or even days of content.

Konami knew that the torture sequence would be the most challenging for players. When starting the infamous sequence where many have witnessed Solid Snake's electrocution several times, Ocelot will give you a warning. If you have not saved for an extended amount of time, Ocelot will ask Snake if he really wants to "travel down that long road again." He is giving you an obvious heads-up that you should probably save right now unless you want to backtrack through hours of play time.

Ocelot's warning is just that: a warning. You don't have to listen to him. But you really should.

10 Technology Has Come a Long Way

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In the early days, when video games were being released on disc instead of cartridges, CD cases were thick. Not only did these bulky cases include instruction manuals, but they also had multiple discs to keep track of. After playing through hours of Metal Gear Solid content on a CD, you would be prompted by various characters to swap out the disc. This was essential if you wanted to continue your game.

Things had changed by the release of Metal Gear 4 and the PlayStation 3. Metal Gear 4 was still physical only at its release, but it only contained a single disc. Towards the middle of the game, your buddy Octacon will tell Snake that it's time to change the disc to continue the game. He will realize Metal Gear 4 is a Blu-ray disc and there's no need to swap it out.

The days of disc swapping are over and now you don't even need a physical disc since digital downloads exist.

9 Looks Are Deceiving

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We first meet Raiden in Metal Gear Solid 2: Sons of Liberty. You might have been angry to hear you wouldn't be playing as Snake, but as a handsome youngster instead. Konami proves looks can be deceiving, as he has a long history as a child soldier under his adoptive father, Solidus Snake, and as mercenary named Jack. His history has gained him various nicknames, such as Jack the Ripper and White Devil.

His body has gone through extensive cybernetic experimentation. The cybernetic parts have not removed the memories of the bloodshed he caused. We learn more of the haunting memories of his time as a ruthless killer, which can be seen in Metal Gear Solid 4 and Metal Gear Rising: Revengeance. These memories are obviously heavy on Raiden's heart and have caused him to have more of a solemn personality.

Even Raiden has noticed the change. He judges himself less and turns his life around from that of a heartless killer to providing for his family.

8 Country Before Self

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The Metal Gear series has always strongly stated that nothing is more important than your country. Families are broken, lives are ruined, and families are broken in order to protect the country's interests.

Metal Gear Solid V: The Phantom Pain proves this in secret tapes found at the end of the game. Players learn that Kazuhira Miller is seen as a person working only for his own self-interests and not his country. He soon gains the nickname "McDonell Benedict Miller," for Benedict Arnold, a man known in American history for being a traitor to his country.

Why would Miller deceiving everyone? You may wonder if he wanted to retire in a large mansion, surrounded by expensive trinkets and driving fast cars. Miller's intentions are simpler than you think. It is revealed that he wanted the money in order to to make the perfect hamburger.

7 Examine Every Inch of Your Surroundings

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In Metal Gear Solid: Peace Walker, you are tasked with finding a truck carrying nuclear bombs in the Mount Irazu parking garage facility. This seems likes a serious mission, but don't forget that this is a series created by Kojima. There are serious moments, but there's also plenty to laugh about.

There's a bunch of trucks to examine, but don't get tempted to rush through this area. Examining the license plates will display many hidden messages. There is a reference to Shina Gawa, a harbor town in Japan. Another truck shows Mei Ling, along with her Codec frequency. More trucks display actual Metal Gear images, which will make Snake react with "Metal Gear?"

One truck may catch your eye because it features a smiling picture of Kojima. The license plate even states his birthdate, 63824 or August 24th, 1963. Once you find this truck, you'll be able to recruit Kojima as an engineer at Mother Base.

6 Mental Health is Just as Important as Physical Health

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Old Snake has a new gauge to watch out for in Metal Gear 4. The Psyche meter affects the Life gauge's regeneration. The stress of combat is directly tied to keeping his FOXDIE's retrovirus in check. Old Snake will get various calls from his psychologst Rosemary. In addition to check-ups, she will try to inform you on how to improve your mental state.

If you call Rose, she will comment on the status of your Psyche guage and she will give you tips on how to recover. Repeated calls to Rose with a low Psyche guage will increase her concern for you. She will give you information on battlefield stressors and psychological stress responses such as fear, anxiety, and worry. Rose will also go into detail about PTSD that parallels real-life experiences individuals encounter in the military.

The tips Rose gives can also be applied to real life situations. Who says that video games aren't good for you?

5 Animal Abuse Isn't Acceptable to Anyone

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In multiple games within the series, the player will be reprimanded or scolded for hurting animals. The Metal Gear series is known for its stealth elements, but there is no hiding your animal abuse from your comrades. In Metal Gear Solid 4, during Codec calls Rose will ask Snake to stop hurting animals. If you continue to harm the animals you encounter, Rose will continue to lecture Snake. She eventually gets frustrated and tells Snake he will go through psychological evaluation if he attempts to harm an animal again.

Hurting animals in Metal Gear Solid V: The Phantom Pain will increase your Demon Points, but helping animals can lead to helpful awards. In the warzones of Afghan and Angolan, there are several animals at risk of getting killed. The Diamond Dogs and Venom Snake are asked to bring the animals to Mother Base. This will increase your Heroism Points plus valuable rewards, such as blueprints and cash.

4 Mirrors Reveal Shocking Truths

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As you make your way though Metal Gear Solid V: Ground Zeroes, you may realize you don't often see your reflection. If you were able to check out your rugged face on every surface, you may be spoiled on a major plot point.

The character Big Boss first debuted in Metal Gear as Snake's main contact and commanding officer. He appears again in Metal Gear Solid V: Ground Zeroes, where he survives a helicopter crash with an unnamed medic and Kazuhira Miller. The medic loses his arm and has shrapnel lodged in his body. Both Big Boss and the medic are both in a coma for years. During this time, the medic underwent brainwashing and facial reconstruction to resemble Big Boss.

Not only would mirrors uncover Venom Snake's true identity, but also that of his hospital roommate, Ishmael. Ishmael's true identity is revealed to be the original Big Boss.

3 Photos are Mementos of Pain and Regrets

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Paz Ortega Andrade is first encountered in Metal Gear Solid: Peace Walker, but she reappears in Metal Gear Solid V: Ground Zeroes. Unfortunately, this is the last game she has an active role in. After her sacrifice, it can be seen that Venom Snake still has his regrets that he was not able to do more to save her.

Paz makes an appearance again within Metal Gear Solid V: The Phantom Pain, but only as a hallucination. Memento Photos are important items within the game and can be found on former Militaires Sans Frontières soldiers. These photos are all related to Paz. After you collect all ten photos and the final eleventh photo, you'll complete Paz's side story.

You will soon realize they aren't just pretty pictures. The final Morpho Butterfly photo is also a metaphor for her death. "Morpho" is also the code name of the pilot of the helicopter that crashes with Paz onboard.

2 Beware Good Fortune or Death From Snakes

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In Metal Gear Solid 3: Snake Eater, there are three silver snakes representing the "sons" of Big Boss: Solid Snake, Liquid Snake, and Solidus Snake. These snakes can be found in Rokovoj Bereg near logs during The Boss fight. The snakes are difficult to capture, especially in the sea of white flowers, but can be consumed.

Though she becomes an enemy, The Boss was an important character in Metal Gear Solid 3. She was not only a well-known American soldier, but also a mentor and leader to Naked Snake. In the final battle with The Boss, she will reveal a large snake-snaped scar running across her body. This snake was due to giving a c-section birth on the battlefield. She compares the pain to that of a snake slithering across a body. This could be seen as a metaphor to a certain Snake causing her pain on the battlefield.

1 Hideo Kojima Really Does Appreciate His Fans

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In Metal Gear Solid V: Ground Zeroes, players can find hidden Metal Gear title logos. When these logos are found, they will disappear before your eyes. This may have been a metaphor for Kojima's own removal from the Metal Gear Solid V: The Phantom Pain and Ground Zeroes after leaving Konami. Konami made sure to erase his presence, just as the logos are erased when you find them.

After finding more logos, KAZ will mention on the radio, "You might be able to erase the marking, but the memories will never disappear." As you continue your logo hunt, you'll eventually hear a radio message from Kojima himself, "You seem to be a fan of Hideo Kojima games. Thank you for all your support."