Revealing mistake: When Bobby's wife is dragged to her knees by the chain, you can make out the shape of her knee pads under her trousers. (00:41:10)
Continuity mistake: After killing all of the assassins, Frank places bullets in a frying pan and turns the stove on. When the bullets go off, the rest of the assassins start shooting at the house, destroying a snowman on Frank's porch. In all future shots of the porch afterwards, not only has the snowman disappeared, but there's also no sign of the snowman's remains either. (00:09:05)