The Japanese version of the game had to edit its torture scene to utilizing "Laughing Rods" instead of shock rods because of the censors demanding they do so to maintain their "C" rating (ages 15 and up).
In North America and Europe, some items had to be changed because they were real world products (even though one of the products, Pepsi NEX, was not actually available outside Japan anyhow).
Enforced Method Acting: David Hayter said that he actually vomited in the sound booth in order to produce some of Snake's choking sound effects for the game (Kojima Productions Report Session 117).
Fake Nationality: Due to the "independent from any nation" spirit of the Militaires Sans Frontičres, the fake accents vary:
Canadian Tara Strong voiced the Costa Rican Paz Ortega Andrade. She also uses a pseudo-Russian accent for Pacifica Ocean.
American Vanessa Marshall voiced the British Dr. Strangelove.
American Catherine Taber voiced the Parisian ornithologist Cécile Cosima Caminades. As a result, when her character had to actually speak French, she would simply sound like an American woman attempting French.
American Grey DeLisle voiced the Nicaraguan Amanda Valenciano Libre.
In English, Miller's voiced by... no, not Cam Clarke, but Robin Atkin Downes, a.k.a. Travis Touchdown and Medic. His delivery is pretty darn similar to Clarke's Miller, though. There's also some Fridge Brilliance in not casting Clarke: Clarke never voiced Miller himself, but an imposter posing as Miller.
Strangelove is voiced by the same voice actress and model of Raging Raven, Yumi Kikuchi, in Metal Gear Solid 4. On a related note, Strangelove is also voiced by Vanessa Marshall, who voiced Olga Gurlukovich in Metal Gear Solid 2 (whom she bears a slight resemblance to), and EVA in Portable Ops.
Donna Burke, the singer who sings "Heaven's Divide" is the voice of Raising Heart.
Ramón Gálvez Mena is voiced in the Japanese version by Agent Smith.
The AI weapons are Hatsune Miku. They use Vocaloid voice synthesizers, but it's the voice of Yumi Kikuchi and Christine Kogure in the Japanese and English versions, respectively.
Relationship Voice Actor: Both Akio Ohtsuka and Mugihito (the respective Japanese voice actors of Snake/Big Boss and Hot Coldman) had also voiced and interacted with each other in Mega Man X 7, playing Red and Sigma.
Shown Their Work: Aside from the usual Metal Gear research posturing, Strangelove wears men's clothing, as indicated by the buttons being on the right side (as opposed to the left).
Talking to Himself: In the English version, the Chairman of the Joint Chiefs and the Deputy Secretary of Defense are both voiced by J. Grant Albrecht.
Teasing Creator: The only possible explanation for the two "date" missions. Hideo Kojima is laughing at all of us. Fortunately, we can laugh along with him.
Kojima originally had no intention to direct Peace Walker. He intended to write only a rough outline of the game's plot and leave the rest to his younger staff, much like he did with the previous PlayStation Portable games in the series (the Acid series and Portable Ops), but he changed his mind when his younger staff did not understand the story's theme of nuclear deterrence.
A dinosaur version of Metal Gear RAY, named Gear RAY, was supposed to appear alongside Gear REX during the Hunting Quests.
The train that Snake was supposed to stop the shipment of nukes by the Peace Sentinel was originally intended to be a playable level. If the storyboards are of any indication, that train would have ended up being shot off the tracks and plummeting.
Peace Walker was originally supposed to heavily resemble Metal Gear REX, down to the rail gun and even the design of its hangar was supposed to mirror REX's hangar on Shadow Moses.
Paz and Zadornov would have been discovered earlier to not be trustworthy (especially Paz), where Paz and Zadornov are overseeing its construction, and Big Boss discovers their affiliation to the Peace Sentinel by eavesdropping from a window in a manner very similar to how Solid Snake eavesdropped on Liquid Snake and Revolver Ocelot's conversation in Metal Gear Solid before Coldman finds and surrounds him. Coldman was intended to be killed by Zadornov alone with a gun to the head, and at some point later, Paz would actually do the very same to Zadornov before hijacking ZEKE. If some of the storyboard sketches are anything to go by, Big Boss was apparently going to actually lead his troops on a sneaking mission rather than going in alone. An entire character model, the AI lab workers, who were implied to be of German origin, was also cut.
Write Who You Know: Cécile is a based on the former communications manager for Konami Paris, Cécile Caminades, in name and appearance.