Have you ever looked at a caterpillar crawling? They kind of look like waves, with the caterpillar moving its back legs first and then the rest of its body following. But this isn't true. I read an article about this in Smithsonian magazine. Some scientists at Tufts University used x-rays to look at hawkmoth caterpillars while they crawl. The actually throw their insides forward, and then the rest of the caterpillar follows. They call this mechanism "gut sliding." It's pretty interesting.