Continuity mistake: When John Travolta and Samuel L. Jackson are fired at in the apartment, the bullet holes are already in the wall before the gun is fired.
Continuity mistake: When they are giving Mia Wallace the adrenaline shot, they mark her chest with a red magic marker. When the shot has been given, the red mark has disappeared.
Continuity mistake: At the beginning, when Brett is initially shot by both Jules and Vincent after Jules' Ezekiel speech, we see Jules' gun becomes empty on firing the last shot. However, on returning to the same scene at the end, when Jules and Vincent shoot Brett the gun does not empty; in fact Jules is able to repeatedly shoot the guy who comes out of the bathroom afterwards and the gun still isn't empty.
Visible crew/equipment: When Vincent enters Mia's home for the first time, a camera and a camera operator are visible in a reflection on the windows in front of them. They have a black blanket or tarp covering them to make them harder to see.
Continuity mistake: When Vincent is shooting up, we see him taking out and assembling his special chrome-plated syringe. In the following close-up of the actual shooting-up, the syringe is a standard disposable plastic one.
Visible crew/equipment: When Vince and Mia get back from Jack Rabbit Slims, and Mia is putting on the music, the shadow of a person walks past her on her left, but Vince is standing still in that scene.
Continuity mistake: When Mia and Vincent arrive at Jackrabbit Slims, they stand in front of a desk and confirm their booking. Throughout her exchange with the 'greeter', Mia's fringe is swept to the side, looks a bit greasy, and is separated. When they go to walk to their table in the next shot, it's suddenly perfect and covering her whole forehead.
Continuity mistake: In the flashback with Christopher Walken, we see him hold up the watch, and its hands are clearly pointing in different directions. But when we see a close-up of the watch, it is set to 12.
Continuity mistake: When Butch is driving the Honda to and from getting his watch at his apartment, from the inside of the Honda the windows are opaque and dirty and hard to see through, but shown from the outside the car windows are clean and you can see through them.
Revealing mistake: In the scene where Lance opens his front door to see Vincent driving across his lawn, with an over-dosed Mia inside the car, the car passes to the left out of view, then we hear the sound of it crashing to a stop against the house. Lance goes outside to see just that as Vincent carries Mia out of the car. If you look at the wheel marks on the lawn, you can see that the car has in fact driven past the house, and out of sight, and that the car in which Vincent and Mia came from was already obviously there already in "crashed mode".