After the fight on the beach and seeing the approaching storm, Duke's clothes are instantly dry, despite being only a couple of minutes after swimming from the boat.
At minute 1:22:56, something is showing where the 6 headed shark is supposed to be. It looks like something with three nipples attached to it, whatever it is, it isn't a shark.
At minute 1:23:15 a piece of equipment is showing in front of the shark. The equipment appears to be whatever is being used to make the shark move it's heads.
The huge approaching tropical storm that was supposed to swamp the entire island, necessitating the survivors seeking shelter first in a floating laboratory and then in a light house, never materializes and is not referred to again once the floating laboratory is abandoned. Instead, at the end of the film, the sun is shining brightly.
After Duke, takes out one the shark's heads, he references his wife, Angie when in the movie his wife's name is Daphne. Angie is Kip's wife.