Continuity mistake: The mailbox is roughly parallel to Richard's SUV but is more perpendicular when he looks at the address number, then it is back to parallel. (00:06:40)
Deliberate mistake: Richard falls (or is pushed) into the lake, and a loud splash is heard. However, as he pulls himself onto the deck, no water drips from him. But there is already a large wet area further onto the deck when the sheriff tosses him. (00:18:05)