The mask of the monster suit was altered considerably. When Ray Corrigan was fitted for the monster suit, the mask was initially too tight. Paul Blaisdell, the maker of the monster suit, had to remove and rebuild the monster's lower jaw so the mask would fit better. Unfortunately, Corrigan's chin stuck out through the opening made in the mask. Blaisdell made up Corrigan's chin to look like the monster's tongue. The mask's original eyes (large and catlike, a Blaisdell trademark) were also removed so that we see Corrigan's own eyes behind the mask.
According to director John Carpenter, filming took only six days. Carpenter didn't direct this film but he was acting as a co-host in an interview with Robert Osborne prior to it being shown on the Turner Classic Movies channel.