Continuity mistake: When Jules enters the apartment, the Big Kahuna Sprite cup changes the direction it's facing in the following shots.
Continuity mistake: When Vincent and Jules are at Brett's apartment at the beginning of the movie, Jules takes the hamburger from Brett's table after he asks to taste it. The hamburger in the first shot simply contains cheese and ketchup, but when Jules bites it there is only a leaf of lettuce. Moreover, the hamburger appears first intact, but in the next shot it appears already bitten.
Suggested correction: The cheese is there when he bites into it, and there is only a piece of lettuce sticking out on one side, a side you don't see when he picks it up. You also can't see if there already was a bite taken out from that angle. My guess is, it's the same burger, no reason for it to be otherwise. When it only "appears" intact, it doesn't mean it is.
Revealing mistake: In the iconic Big Kahuna burger scene, Brett gets shot in the shoulder, a normally highly debilitating injury. However, in the frame before he is killed, he throws back his arms with the ordinary range of flexibility, and it becomes obvious that the actor's mobility is not really impaired, and he was only faking an injury.
Continuity mistake: When Yolanda is standing on the counter during the robbery, she gets so upset while screaming at Jules that she has a big blob of spittle on the left side of her chin. We cut away and when we cut right back, the spittle blob is gone.
Continuity mistake: After being sprayed in the face with water while tied up in the basement, the next shot shows Butch and Marcellus Wallace having no water anywhere surrounding them on the ground.
Continuity mistake: When Butch crashes and Marcellus shoots the woman, there's a second woman next to the door, and a white cup next to her. In the wide shot the cup is gone.