Don't Bug the Mosquitoes - S2-E12
Other mistake: The 4 band members, all their equipment, months worth of food supplies, I am assuming medical supplies, change of clothes and other sundry items all magically fit into a small two seat helicopter.
Gilligan's Living Doll - S2-E21
Other mistake: When the Howells give their suggestions, if you look at the dark rectangle, you can see the word REJECT before it lights up. Likewise, when Ginger talks to it, you see TILT before it lights up.
Other mistake: When Gilligan and the ape are staring at each other, with the idea that the ape will stay hypnotized and ignore everything else, look closely at the ape's eyes. The actor in the suit glances twice and the Skipper and Professor as they pass.
Other mistake: Mary Ann comes up to the Skipper while he's learning to juggle. If you look closely, the coconut bounces on the ground a couple of inches from his left foot. When Gilligan approaches, the coconut bounces off the bottom shelf. And in both times, the Skipper reacted in pain.
Other mistake: When Mrs. Howell looks at the lion in the mirror, the image is not reversed as it should be when the camera looks directly at the lion.
Other mistake: All of their sheets were the same type. The sheet that the "Ghost" supposedly took from them was more silken, not the regular knit.
Other mistake: In the opening scene, and later, the camera shows the Howells' hut, but the scene is in Skipper and Gilligan's hut.
The Friendly Physician - S2-E29
Other mistake: The whole time the control for the booths is operated, the handles are pulled towards the camera. In the final lab scene, Gilligan flips the lever towards the camera, but you can see the indicator reads 'OFF'.
Answer: Hungarian-to-English translation aside, Erika's log-book entries were utterly meaningless. When the radio interviewer expresses confusion, Erika even reads entries from the log: "You take a left at a big, beautiful, pink tropical flower, then pull over and park," and "After the storm, we backed up and made a U-turn," etc. Her directions were scatterbrained, to put it nicely. Additionally, Erika's yacht was forced to leave the island during a tropical storm, and they lost their bearings for several days before the Navy found them. Given that Erika was such a scatterbrain, we might also assume that she didn't hire the most competent yacht crew, either.
Charles Austin Miller