The Gelminator 6000 was designed by Gus ever since he first met Gelman, but it was built when he got a fortune that told him that he will be facing his last day (thankfully, this is soon disproved). The Gelminator 6000 worked great, but in a twist of fate, it trapped Finster instead of Gelman. Gelman is nonetheless shaken. Finster gives Gus detention for until 8th grade, and the Gelminator gets disassembled.
The Gelminator works when someone like Gelman steps on an inflated hot water bottle with a cue ball stuck in it. The cue ball will shoot up and hit a wooden target, thus setting off a rope mechanism that brings down a large colorful cage down on the victim, trapping him/her. An addition, such as a cloth sign that says, "Don't feed the Gelman, Remember Gus Griswold" (sic) can be added for effect