Space archaeologist Simon Watterman (Harvey Korman ), discovers a fossilized “Munchie” in a cave in Peru. Bringing the specimen back to the United States, Watterman’s son Paul (Charlie Stratton) and girlfriend Cindy (Nadine Van der Velde) accidentally reanimate it and name it Arnold. Cecil Watterman, Simon’s evil twin brother and snack food entrepreneur, kidnaps Arnold while Cindy and Paul are making out.
When Arnold is hurt by his kidnappers, it becomes aggressive and attacks Cecil’s adopted son. Attempting to kill Arnold, they chop him into quarters, but instead of dying, Arnold multiplies into four new munchies (some voiced by Frank Welker). The quartet of creatures develop a love of women, beer, attacking people, and junk food in the process.