Continuity mistake: As they struggle with the sail, Skipper's hat is backwards. After a shot of the shark, his hat's on right as he tosses the sail.
Continuity mistake: After the shark bites off the rest of the paddle, leaving the handle, Gilligan hesitates a second, sees no paddle, and begins swatting at the shark. A moment later, in the closeup, he's paddling, hears the bite again, and pulls the handle up, showing the paddle is gone.
Continuity mistake: As the rock that triggers the trap is pulled, the vine used slides completely off it. In the wide shot, the vine is securely around the trigger rock.
Continuity mistake: After the shark bites Gilligan's paddle and he holds it up, the amount of wood between the handle's connection and the bite differs from shot to shot.
Continuity mistake: At the beginning of the episode when everyone is listening to the radio the professor is shown standing up and in the next shot is sitting down. (00:02:50)
Answer: Bob Denver answered this when he was on a talk show hosted by Pat Sajak. He said they were going to write into an episode where the castaways found all these clothes, but it got too complicated, so he said, they decided, "who cares, it's only a TV show," and forgot about it. So the writers and actors even asked this, they just never bothered to address it.