Continuity mistake: When Harrison Ford and Anne Heche come out of the cave they fell into, Anne has a scorpion on her head. If you look closely you will see that it is just a toy and much smaller than the real one we see in the next shot.
Continuity mistake: When Robin is changing her clothes, after the scene in the water where "something swam up her shorts", she is actually changing out of the clothes she was wearing when the plane crashed, not the clothes she was wearing in the water.
Continuity mistake: When Anne Heche is standing in the water and Harrison Ford is trying to dig the "creature" out of her shorts, the mud on Anne's face keeps changing. In some shots it is gone, in some there is a little and in some there is quite a bit.
Plot hole: After running from the pirates, the two castaways almost stumble off a cliff. Unless they were running backwards, I'm sure they would have seen the cliff coming for a while, because when the camera zooms out you can see clear terrain for at least 20 metres until the edge of the cliff.
Continuity mistake: When Robin stumbles upon a wild pig, she is pretty close to wading in to the water in the lagoon. Yet in the next shot, she stumbles down a little hill for quite a way before she gets to the water.
Factual error: When the aircraft crashes on the island, the front of the aircraft strikes the ground which would have bent the propeller. They would have never been able to fly it again with that prop.
Continuity mistake: When Robin and Quinn are standing on the cliff she is afraid to jump, he kisses her and in the shot facing him he has his hands on her face while he is kissing her, but in the reverse shot his hands are not on her face. He didn't have time to move them between shots.
Continuity mistake: While they are approaching, and then running from, the pirate ship, in one shot the horizon is completely empty. Then, in the next shot, the ship is back. This happens more than once.
Continuity mistake: When Frank is seated at the nightclub where Angelica performs, watch the light and flowers on the table. When he is seated the light is sitting in the center of a bunch of flowers. Next shot, the flowers are almost gone and the light has moved a good foot or so.
Continuity mistake: Angelica and Frank get in a helicopter to join the search of Robin and Quinn. In the meantime, a day has passed on the island. We come back to Angelica & Frank who are in the helicopter wearing the same perfectly neat clothes as the prior day.
Continuity mistake: When Harrison Ford and Anne Heche climb up the hill to turn off the beacon, you can see that Harrison's shirt has a few buttons unbuttoned from the top. We can see one button but the other is covered. When Anne asks "Who stole the peninsula?" we can see both buttons.
Other mistake: Watch Harrison Ford's hair throughout the film. When they are making the rafts out of the plane, you can see that he has had his hair cut. I never knew that they had a barber's on that island.
Other mistake: When Quin is cutting the plane that's stuck in a tree, he uses a saw, that looks brand new. He's just been chased by pirates and jumped off a cliff - where did he get the saw from? Anything in the plane would be rusty by this point.
Continuity mistake: When Angelica is doing her sexy dance for the tourists, her anklet changes legs between the close up shots of her feet and the far away shots of her.