When Eileen returns home from the FBI and checks the mail, two identical looking business letters are visible that both have "Pittsburgh, PA" spelled without h in the recipient address. On the first letter the same mistake can also be seen in the sender address.
When both men are climbing through the woods, Wayne pauses to rest, and Arnold cocks his handgun and discharges it, aiming for, and hitting the trunk of a nearby tree, to show that he means business. The sound overdubbed is the distinctive sound of a hammer being locked into position, consistent with a revolver, but the handgun Arnold is holding is actually small automatic. The sound effect should be that of a 'rack and slide'.
When Wayne is leaving the table by the pool, he picks up his jacket. In the next scene just a second later, he picks up the ball to the throw to the dog and his jacket is on. There is no way he would have had time to put on his jacket.