As everybody knows, everything is worse is Soviet Russia. That especially applies to the prisons. But this is Snake we're talking about: he spent the whole game before this eating raw animals and killing Spetznaz in the jungle. He sets the manliness bar pretty high by default. So to make things interesting, they tortured him, tore out one of his eyes, took all his stuff, made him shirtless, and gave him nothing but a fork.
True, he had some other items to work with, but there's something about giving him something so seemingly harmless as a fork that lets you know, immediately, that he is about to do really nasty and awesome with it. And what do you know: Snake breaks out of prison and goes on with his mission like nothing happened. Because that's what Snake does, Smash Bros invitation or no.