During a 1978 interview on The Tonight Show with Johnny Carson, Bruce Dern revealed he was not paid for his role in the film. He was issued a check for $1,700 during filming, and when he went to the bank to cash his check, the check bounced. When he returned to the set on the next day scheduled for filming, the set had already been shut down.
Casey Kasem was a big name in radio, and during the 60's was one of the top talents on 1110 KRLA on Los Angeles airwaves. A fellow DJ was the very popular Dave Hull. The "Hullabalooer" (as he was known) can be heard in this movie providing the voice for a radio announcement.
When Bruce Dern is showing Casey Kasem his two-headed animal experiments, they are, of course, cheated to look like they have two heads: these include a monkey, fox and rabbit. The one experiment that he shows (and that we see) closeup is a two-headed snake. The reason is, two-headed snakes actually exist.
The following year, The Thing With Two Heads came out, and although low budget, it's mainstream compared to this movie. Both center on a scientist who creates a two-headed human: Each have a really big and tall guy's body with the added head of a shifty, evil antagonist.
Pat Priest gained fame on The Munsters as Marilyn, the niece of a character in the image of Frankenstein's Monster. And here she co-stars with John Bloom, who played Frankenstein's Monster in Al Adamson's Dracula Vs. Frankenstein.