The episode: “Gamera vs. Guiron,” ep. 312
The riff: Monotoned by Joel as some weird, lumpy asteroid-type things fly toward a spaceship being piloted by our boy heroes.
The explanation: This is a reference to a series of pre-show “policy trailers” by the Midwestern theater chain General Cinema, which existed until 2002, when it was bought out by AMC. In one of the spots, various snacks like popcorn and soda would fly through space just like the asteroids, eventually flying into a garbage can. I think it can probably be assumed that there were some General Cinema locations in Minnesota when the show was being filmed.
Novelty factor: I’ve never even heard of General Cinema, much less this particular bumper. I am actually rather amazed that I was able to find the exact video in question. YouTube never fails to amaze. Who is uploading these things?