So I was alone, playing Rock Band about a week ago, and there was a cat nearby, ostensibly asleep. In between songs, I noticed it doing something odd: it was standing up, head sticking out over its bed, thrusting the length of its body forward and backward, over and over. Its difficult to describe the impression of extremely mechanical motion that this gave, but I'll try.

Each movement forward and backward was accompanied by the head moving up, or down, respectively (edit: not really moving up or down, so much as rotating so that it was pointing up or down; again, it's hard to describe); the feet didn't move, and the tail seemed not to, despite the way the cat's torso seemed to be propelled back and forth. Eventually, as the cat moved back and forth, it started making a noise along with each downward movement of the head. It was a deep, guttural noise, which strongly implied that the cat was going to throw up. This noise slowly got louder and louder until there was one final, relatively loud noise and thrust... and nothing happened.

Then, within a minute, the cat started doing to the same thing. The noise started sooner this time, but the movements were exactly the same: back and forth, back and forth, extremely mechanical. This time, though, after about 20 seconds, it did, in fact, throw up.

This makes me wonder: were the movements just the cat-equivalent of the dry heaves a person might experience one or two of before throwing up? Or, do cats need some sort of momentum-build-up before they can eject matter from their stomachs? Furthermore, do other mammals have other, dissimilar, vomiting movements they can, or must, make when they need to eject what used to be foodstuffs from their bellies?