When Willy comes out of his flashback in the bathroom of Frank's Chop House, the close up shot shows a drink on the toilet seat. When the shot shifts behind the entering waiter, the drink is gone.
When Willy sits on the chair 120 minutes into the movie, Biff throws himself down at his feet and clutches his shirt. In one shot, Biff has his left arm on Willy's right shoulder outside his arm, in the next shot, he has his arm on Willy's right shoulder inside his arm, in the next shot he has it outside his arm again.
When Biff and Linda argue in the kitchen, Linda grabs an empty glass and places it under the tap, when she turns the tap on no water comes out but when she picks the glass up, it is full of water.
When Willy is playing cards with his neighbor, the cards he's holding change between shots.
When Willy is talking to himself, drinking milk, the level of milk changes in his glass before he takes a drink.
Hap gives Linda flowers after his night with Miss Forsythe and Letta. Linda crumples them and throws them down. Biff picks them up but they are destroyed. Another scene later,Willy is putting flowers in a vase the same color.