Continuity mistake: When Jay and Silent Bob are running away from Lefours and hide by the table Brodie and TS are sitting at, check out the positions of everyone - Jay and Silent Bob run on from the right side of the screen, across to the left side of the screen, and duck down behind the table, just as Lefours comes on from the right side of the screen, where he looks around, failing to see them. The layout of everything means that he would have been able to see them the whole time they ran across the screen.
Continuity mistake: When Brodie sees Rene in the clothes shop and he says "that would look terrible on you", Rene is holding a jacket. Then they walk to the next rack and the camera changes. She now has a brown jacket folded on her arm. They walk to another rack and the camera changes again and she doesn't have the coat under her arm.
Continuity mistake: After T.S. and Brodie talk to the psychic, they return to the mall. On pulling into their parking spot, there is a Red Yugo on the driver's side and a Green sedan on the passenger's side. In the very next shot, when they get out of the car, there is a Green Taurus on the driver's side and a Black truck on the passenger's side.
Continuity mistake: When TS and Brodie are sitting in the food court, as Jay and Silent Bob are running from Lefours, the cup TS is drinking out of is white on one side with the logo for Diet Coke on it, and red with the logo for regular Coca-Cola on it. First the white side is shown facing outwards (from TS), then the red one as Jay and Silent Bob run past, and then back to the white for the close-up. He did have the time to turn the cup around while not on camera the first time, but not the second.
Continuity mistake: After Silent Bob crashes through the poster and bursts in on Joey Lauren Adams, it shows an outside shot of him kneeling on the ground, head through the poster, with the rope slack next to him. For the rope to be slack in that position, when he was hanging downwards he would have been significantly lower than that, but if he'd swung up from that position then he would have smashed his head on the underneath of the walkway rather than arrived above it.