Those of us who work on and grow the crops they eat may think of tobacco hornworms (Manduca sexta) as pests to be controlled, but they are also import lab rats for all sorts of biological research. In fact, my undergraduate research studied hormone binding and transport in M. sexta in response to environmental stresses, so I have dealt with my fair share of hornworms in and out of the lab.
A recent study used hornworms as a model of locomotion and found that their gut and body move separately! See here for a nice summary and cool video!
ScienceShot: Caterpillar's Guts Crawl Independently of Their Bodies