26. Parrots
There are two parrots in the Metal Gear Solid series; one belongs to Otacon's younger sister, and cannot be killed, whereas the other is the only friend of The End, the ancient sniping genius. The End's parrot can be shot and eaten. That is all.
25. Solid Snake's Bandana Grants Him Unlimited Ammo
In MGS2, while launching the final assault, Snake gives Raiden a bunch of supplies and ammunition. Raiden looks back at him and asks if he'll be alright. Snake responds that he'll be fine, points to the bandana on his head, and says, "infinite ammo". This is a tongue-in-cheek breakage of the 4th wall, which is a favourite pastime of Hideo Kojima. Interestingly, players can actually unlock the bandana as an item, which grants unlimited ammo when equipped.
24. ID Guns Are A Real Thing
Gun bio-metrics are a way for Metal Gear Solid to prevent players from getting their hands on the superior firepower of their enemies. The explanation is basically this: modern guns have sensors that read the user's nanomachines, and if the gun's tag matches the user's profile, the gun will unlock and be ready for use, but if there's no match, the gun is not usable. While this might seem like a cheap way to force players into using their piddly tranquilizer pistol, this is actually a real military development, and something similar was also seen in last year's movie Skyfall (albeit opting for a palm print rather than nanomachines).