Cabot's helicopter has a different paint job than the unconvincing model of the helicopter which explodes after it takes off from the island.
When the woman is being assaulted under the pier, a creature kills the gangsters that are attacking her. The first criminal to get killed gets his neck broken before being tossed aside. While he is getting his neck broken, you can see his mustache and stubbly beard. When he gets tossed onto the beach, his stunt double has a different hair style and no facial hair at all. The same shot of this stunt fall is reused about 20 seconds later to represent a different punk getting beaten up.
When Ellen Jarvis throws the tell-all book into the fireplace, it is very noticeable that the book is actually made of two smaller books, one with yellow-edged pages and one with green-edged pages, that have been put together into one book cover.
When the creatures hijack the boat and Stephen Jarvis is giving his voice over, there is a long shot from above. The shadow of the camera helicopter can be seen passing over both the boat and the water.