From Muppet Wiki

Dr. Tucker is the sadistic scientist in charge of medical research at C.O.V.N.E.T. in Muppets from Space. Rizzo the Rat ends up in his lab and, along with Bubba, Fast Eddie, Troy, Shakes, and The Birdman, is subjected to Dr. Tucker's grueling tests, including a maze, a centrifuge, and an air tunnel. The exact purpose of these tests remains unknown.

Dr. Tucker enjoys treating the lab rats cruelly and often taunts them with promises of cheese and reminders of how futile escape attempts were, before Rizzo helps them break out of the lab.