When Sully catches a ride with Peter and his family, Sully asks Peter if he's still teaching somewhere. Peter confirms that he teaches at "University of West Virginia." That university's actual name is West Virginia University.
After Sully and Peter break into Tip Top Construction and drive off with the snowblower, they stop by the house on Bowdin Street and talk about the place through the rain streaked windshield, yet the snowblower is nowhere to be seen in the back of the truck.
When Sully pulls up to his old home at night alone and stares at the house in his headlights, it isn't snowing as it was when he pulled in, and as he leaves it is snowing again but going up in the sky - it is the arrival clip in reverse
After Officer Raymer is punched in the face by Sully, he collapses to the ground against his car with his head in front of the Police seal on the door. When the camera pulls back, Raymer's head and body are positioned a good two feet to the left of the Police seal.
Throughout the movie, Peter always wears glasses; he is obviously substantially nearsighted. But when Peter, Sully, and Wirf are at the bar discussing plans for Sully to go to jail, Peter has removed his glasses. After the discussion, Peter falls asleep. The moment he wakes up, he throws on his coat and walks out without picking up his glasses. In the next shot Sully and Peter have just left the bar, and Peter is once again wearing his glasses.
When Sully and Peter are stealing the snowblower from the Tip Top construction yard, Peter has to climb the fence to get in. Once in, Sully throws him a bolt cutter to cut the chain holding the snowblower. Why didn't they just use the bolt cutter to get in instead of climbing the fence? And if that wasn't possible, how did they get the snowblower out?
At the end of the movie, when Sully brings the dog home late at night, the noise awakens Miss Beryl from a sound sleep. She quickly puts on her robe and slippers and emerges from her bedroom with her hair neatly coiffed and wearing lipstick. Nobody wakes up with their hair neat (unless they took measures to preserve their hairstyle while they slept), and no woman in a reasonable state of mind goes to bed with lipstick on.