Other mistake: The brief chess game (four moves) shown in the beginning of the movie makes absolutely no sense. For instance: There are no white bishops on the board, but after the human player taps a few buttons, the computer says that he just moved one. Within the two moves described first, the positions of the pieces change completely. In addition, some pieces are now gone and there are new pieces on the board. It's like an entirely different game. The final move is said to have been made with a black rook, which is impossible. In the shot shown before this move, there is not a single position available to that chess piece that would result in an instant checkmate. Nothing in the editing indicates that these few short shots are supposed to be viewed as separate games. (00:04:50)
Other mistake: There's no way for Shelly to fit his masks, a speargun and other items in the small box.
Suggested correction: No, but we don't know exactly what he might have brought. The first time we see him they're picking up Vera, so it's most likely he brought another bag that could contain the items. He only said to Vera that the small bag was his whole world, but he just met her (Andy mentioned he got him a date for the trip) and he's trying to get her to warm up to him.
Other mistake: The creep tells us that this is the first issue, but mere seconds after the famous ending of Father's Day we see fan mail on the second page, impossible for the first issue. (00:21:05)
Other mistake: The night after burying the bird, a lightning strike projects an image of the tree outside onto the bedroom wall. However, the silhouette has nothing to do with the tree's shape.
Other mistake: Why is it that Marge only discovers the microchip in the Silver Shamrock badge when it drops on the floor in the motel room? Surely she would have noticed it when her son would have thrown the mask against the wall, and it dropped off? Any normal person would have looked at it to see how it would have attached to the mask.