On the one green level where you push the rock down in a straight line then you slither a couple paces left, I just ran into a weird glitch where upon pushing the rock down the line, snakeman kept on moving with no sign of stopping. I tried lettin' go of the down key, and even pushing other keys, but alas, snakeman had some sort of date with destiny. Pressing spacebar fixed it though, because that just undoes whatever move is currently happening. I'm not sure if this glitch is at all replicable though, so it might've just been some sort of fluke.