When they are making the "film," Gilligan, as a "cannibal," ties Mary Ann to the post with horizontal ropes, one below her breasts, one above. When the "film" is shown, though, the ropes are in a "criss-cross" pattern below her chest.
This movie was made so the castaways could be rescued, but how could they be found? The map the Skipper was pointing to didn't have anything on it that could realistically show where they exactly were, and all scenes in the film wouldn't help them get found at all, just made for good laughs.
There's no way silver nitrate film used in the silent era would have been preserved submerged in salt water for 40 years.
While at the lagoon, the Professor and Gilligan are talking to Skipper in his underwear, a car is visible in the background. It is behind Gilligan's left shoulder. The windshield is clearly visible.
It's not explained how they could get far enough out into the ocean to get a full shot of the island (which is obviously the same shot used at the end of the shows, minus the title). And if they could get that far out, why could not get off the island. They were other attempts made just to get out into the shipping lanes.
The movie won the grand prize at Cannes - yet none of the judges, nor anybody else who saw the film for that matter, recognized actress Ginger Grant or millionaire Thurston Howell III, as their "reappearance" would have made headlines worldwide.
Rather than waste time making a "movie", the castaways should simply stand in front of the camera and write out their situation on the blackboard. Someone would also recognize the Howells or Ginger as passengers from the Minnow.
The entire premise of this episode is ludicrous. Rather than mime their supposed experiences on the island for a silent film, all they needed to do was *write* a message and film it. The message could've contained very specific details about who they are, their approximate location, what happened to the Minnow, etc. Once the film was found, and the message read, they'd have been rescued.
Despite knowing it's silent film equipment, they're constantly speaking as if it was "talkie" film. (Big example, the Skipper trying to explain where they are and how they got there by pointing and talking to the camera.)