Snake appears to dislike Sonic according to his Smash Taunt conversation with Otacon when battling the hedgehog. Whilst the reasons are mostly unclear, one popular theory is that it references how Snake's Japanese VA, Akio Otsuka, is the son of Chikao Otsuka, who voices Sonic's nemesis, Doctor Eggman/Robotnik. Coincidentally, Chikao also voices Big Boss in Metal Gear Solid 4. It's also possible Snake's disliking of Sonic is a reference to how hedgehogs eat snakes in the wild.