The sound effect of the hypnotoad is borrowed from the sound effect to Yars' Revenge (1981) looped continuously. David X. Cohen states in this episode's commentary, the sound effect is known as "angry machine."
The pet competition is the only time in the entire series that the Hypnotoad makes an appearance outside of his television show, "Everybody Loves Hypnotoad."
Originally, when Fry observes the effects of the Brainspawn ("Wait a minute, I know what's going on here. You've all become idiots!"), Bender suggests, "Hey, let's all join the Reform party!" Later, when the show was syndicated, the line was updated to, "Hey, let's all join the Tea party!" to make it more relevant.
The alien languages (both 1 & 2) on the obelisks in front of the Nibblonians Hall of Forever (aka Hall of Eternity) translates to Yummy Tummy.
While listing the planets the Brainspawn have destroyed, Hermes says "First the civilization of Space Rome collapsed, then Don Martin III went "kerflooie"..." The first is a reference to the empire of Ancient Rome, and its infamous collapse (the term almost always used to refer to its deterioration and eventual fall). The second refers to cartoonist Don Martin, whose comic strips heavily features onomatopoeic sound effects, like "kerflooie".