When the man comes to blackmail Foss, we hear the door shut. After Foss breaks the man's neck and the camera pans to a medium front of Foss, the door is open behind him.
When Josh and Ashleigh are in the hot tub, the water is glassy smooth. A properly functioning jacuzzi would have bubbling water. The day of the shoot, though, the crew could not get the jets to work. This is discussed in the DVD commentary.