At around 1:35 when Harry is driving Dale home, Dale's cigarette changes back and forth from left hand to right, between shots.
At about 54 mins, when Jen's gotten out of the car, she starts walking and is even with the caution sign on the wall. In the next shot, as Harry pulls away, she hasn't yet reached the sign.
When Dr. Koch suggests that Harry move to West Greenwich he states "I'm not moving to fucking South County". However, Block Island is located in South County.
When harry first returns home, the door on the freezer compartment in the fridge is open and light is shining from inside. A freezer compartment normally does not have a light.
Dale's tirade at the beginning of the movie confuses symbiotic and parasitic relationships which are completely opposite.
Around 01:04:46, when harry picks up the newspaper from the store, it can be clearly see that the back page is blank (unprinted)
The police jackets have a police shoulder patch, but no identifying words, name or insignia on the front or back.
When on Tom's boat and with Tom missing, Chief Rogers refers to Tom in the past tense (as if he is dead) to Harry and Audrey.