Continuity mistake: As Gilligan marches over the cliff, he's wearing Skipper's hat. As he's hanging on the branch, his regular white hat is on his head.
And Then There Were None - S3-E13
Continuity mistake: Whenever one of the castaways falls in the trap and "disappears", there is complete silence when their name is called out, yet when the Skipper falls in (the last of the six), suddenly Gilligan hears all their voices shouting from down below.
Continuity mistake: The professor mentions he can't drink vodka with the Russians because he's allergic to alcohol, yet in the episode "Man with a Net" (with Lord Beesley), he drinks a strong alchoholic drink he made along with everyone else with no signs of any sickness, or reaction preventing him from drinking it.
Continuity mistake: When they are listening to the radio report describing the lost boat, the professor goes from standing up to sitting down between shots.
Gilligan's Personal Magnetism - S3-E21
Continuity mistake: When Gilligan knocks the door off the hut it lands on the Skipper's neck with the life preserver on the top. In the next shot the preserver is on the bottom.
Pass the Vegetables, Please - S3-E3
Continuity mistake: The radiation meter the Professor reads disappears between shots.
Continuity mistake: At the end after Gilligan pretends to throw away the Eye of the Idol, everyone gets up to look for it. As the Professor gets up, Gilligan gestures to him. In the next second, his arms are on the table.
Operation: Steam Heat - S2-E25
Continuity mistake: When Howell is talking to Gilligan, the ground apparently trembles due to a volcano. Before the rumble, Howell's Safari hat brim is bent up on the left side. After the cut to the Professor, the right side is bent upward.
The Producer - S3-E4
Continuity mistake: Harold Hecuba (a.k.a. H.H.) goes out to change costumes. When he comes in as Ophelia the stage door first closes behind him, then falls off the hinges. The shot cuts to the Castaways, then back to H.H., and the door is back on the hinges.
Continuity mistake: When Gilligan falls off of the cliff at the end, he is wearing different clothes and facing a different way than he was when he fell off.
Pass the Vegetables, Please - S3-E3
Continuity mistake: The book the Professor is reading to the others immediately switches from being lower to higher as the scene cuts.
Good Night Sweet Skipper - S1-E5
Continuity mistake: When the Professor drops a couple of tranquilizer pills in the Skipper's cup, it's nearly filled to the rim. As he hides the bottle of pills, the liquid is a little lower.
Voodoo Something to Me - S1-E4
Continuity mistake: As the Professor comes up to Skipper and the girls, his left hand goes up to his face, but a second later it's his right hand on the bridge of his nose.
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: As the raft starts to sink, Lovey goes into the water on the back side of the raft. When the camera is in a close up of Mr. Howell, she's sitting beside him again. Then she's neck-deep in the water in the next wide shot.
Big Man on a Little Stick - S1-E22
Continuity mistake: As the Professor sends Duke off, he gives the island's position as 110° Latitude, 10° Longitude. In "X Marks the Spot" (S1: E: 19), the position is given as 140° Latitude, 10° Longitude.
St. Gilligan and the Dragon - S1-E21
Continuity mistake: As the women are packing up to move out, Mr. Howell says he and Lovey have been married for nineteen years. As the men are trying to get to sleep, he says they were married twenty-two years.
Beauty Is as Beauty Does - S2-E2
Continuity mistake: We see a shot of the outside of Ginger's hut when she and the Skipper are first planning for the beauty contest. The door to the hut has a window in it and we can see the Skipper's hand leaning on the sill. We cut inside and suddenly Ginger is by the door and the window has vanished.
Continuity mistake: After the vampire's wife (Ginger) unfolds the couch bed, she laughs with her arms down and spread out by her sides, but the next shot shows her hands up by her face, clutching her gown.
The Friendly Physician - S2-E29
Continuity mistake: The color of Ginger's shoes are different once returning to the island at the end of the episode from what she wore on the mad scientist's island.
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.