Sega Announces new 2D Sonic title

[Vipershark]

Because it confuses you with other things.
As I sad, everything you do makes it move. Since jumping on it makes it move up and down, the obvious solution is to jump on it until it dips low enough for you to enter it. But as soon as you try to jump off, it shoots back to original position. Thinking that you simply didn't jump enough, you attempt it again. And again. and again.
That's what happened with me. I stopped playing the game for years until I learned what to do.