Caveat

When Isaac arrives at the island in the beginning of the movie, he brings no supplies or clothes for a five day stay; the boat is empty.

48 minutes in, when Isaac is looking at the corpse in the basement through the hole in the wall, he shines his flashlight on her face, and when he shines the light on her eye, her pupil dilates. This would not happen in a corpse. In fact, doctors check pupil dilation to see if a patient is brain dead. And the pupil will already fully relax (dilate) after death.