Other mistake: When the headhunter is about to chop a tree Gilligan is behind, he yells. The actor has metal fillings in his teeth. Headhunters would not likely have a dentist.
Other mistake: As the Skipper is on the ground under the tree waiting for Ginger to get Gilligan, the headhunter is crawling behind him. You can see some smoke in the lower left corner, likely cigarette smoke from a crew member.
Chosen answer: It looks like a mistake to me I see it when the Professor is put into a trance, but it is not there later.
Bowling255 ★