When Sarah hands Hank the glass of water, the water level in the glass is slightly below the top of the ice cubes, with some ice cubes poking up above the water. When Sarah hands the glass to Hank, the ice cubes now only come up to about an inch below the top of the water.
When Hank is finally going through Manny's phone, after he sees his e-mail with the birthday message from his dad, he proceeds to check out Sarah's photos on Instagram and the phone that has 1% of remaining battery changes to 2%.
The red VW Cabriolet seen near the end of the film has the California license plate 1E49950. This is a commercial plate and would not be on a regular passenger vehicle. Additionally, a commercial plate beginning with "1E" would be from the mid to late 1970's and would be on a blue plate, not a modern white plate.
At approximately 33:17, a man with what looks like a red plain shirt can be seen walking in the back ground right above the actors next to the standing tree in the middle of the screen.
About 34 minutes into the film, while Hank and Manny are deep in the woods, what appears to be the roof of a car or truck can be seen in the background on the left side of the shot.
At 34:00, while Hank and Manny walk towards the right hand side of the screen, a man can be seen far away in the background on the far left side.
At the beginning of the film, during the closeup of Hank trying to hang himself, you can see part of the real mainland or rest of the island to the upper right of the screen, revealing it to be far larger than the small island shown during the wide shot.
When Hank sees Manny's body at the shore, he rushes to it and turns it over. He crawls around to the other side to see if he's really dead and accidentally puts his hand on Manny's crotch. Hank quickly pulls his hand away.