In the opening scene, Dr Chopper cuts off the male victim's right hand. When the shot cuts to a close-up on the bowl, however, it contains a severed left hand.
In the opening scene when the three cops burst into Dr Chopper's lab, they are clearly brandishing toy guns.
After the kids almost hit the girl riding the ATV, when the kid in the red jacket stands up, you can see the boom in front of his hair.