When they first try the weapons Paul says to Barabara that only three shots can be held in the shotgun chamber so make each shot count. At the end of the movie when he kills the monster he uses the same shotgun and fires off four shots in a row.
The Outsider slashes the back of Paul's flannel during the fight scene in the tunnel. His flannel and his flesh are clearly torn and bloody. Moments later Paul confronts the homeless lady with the tracking device is her cart, and when he turns to walk away the back of his flannel isn't torn at all.
Paul's hair is all messed up when he asks the guys in the station wagon where he is, then his hair is combed in the next shot.