Patzer

When David is going to confront the villagers about the cat, he lets in four men, but when they gather in the living room, there are only three villagers.

The men open the mantrap for display then ask where to put it. They are asked to hang it above the fireplace. The guns which were hanging there whilst they opened the trap have, in the meantime, disappeared.

After Amy tells David to get some lettuce, David notices the addition symbol on his chalk board changed to a subtract symbol by Amy earlier on. After he corrects her mischief, the symbol jumps from being an addition to a subtraction.

When Amy fires the shotgun at the last attacker both the hammers are in the 'uncocked' position. She would need to pull the hammer of the relevant barrel backwards to cock the gun.

At the start of the film, Dustin Hoffman goes into a village pub and asks for American cigarettes and he's given Rothmans, which are British.It would be highly unlikely for a village pub to sell American cigarettes.

When David is taken duck shooting, he fires his gun into the air at ducks flying overhead. Ducks can then be seen flying to the right and straightaway to the left, revealing that it is the same film reversed.

In the build-up to the crescendo of violence, the thugs amuse themselves by riding on tricycles found in the Sumner's outbuilding. The presence of these tricycles cannot be explained. David and Amy had just come over from the USA, they don't have any children. In the original source material, the book, The Siege of Trencher's Farm, the couple had a child. The tricycles might suggest that they are leftovers from an earlier script, but as it is presented in the motion picture, it is obviously very unlikely that David and Amy would have carted tricycles all the way from America.

Where the addition symbol is changed to a subtraction symbol, the previous symbol in the equation is first shown as a subtraction symbol. When the close up is shown, it is an addition symbol. Throughout the rest of the film, each time it's shown in a long shot, it is a subtraction symbol; in close ups, it is an addition symbol.

As David and Amy Sumner drive up to their house for the first time, the camera crew is reflected in the car's side window.