Revealing mistake: The marks where Jim Backus and Natalie Schaffer are supposed to stand are some unnaturally positioned twigs in the sand during the scene of Mr. Howell's practice polo pony stuck in the tree.
Revealing mistake: After Gilligan lies down on his hammock, there is an "X" in the sand where actor Alan Hale, Jr. stands. Obviously it is the mark where Hale is supposed to stand, and he does stand there as he speaks to Bob Denver.





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 ★