Continuity mistake: When Lloyd drops Mary off at the airport and hugs her goodbye, in the background there are two men walking towards them. The camera changes to the angle behind Mary then behind Lloyd and then back to the side. When it returns to the side view the two men are farther away but still walking toward them.
Continuity mistake: When Harry and Mary go out on the date to the ski resort, when they get into a snowball fight, the camera shows Harry, and it's snowing, but when they show Mary (who is supposed to be right beside him) it is not snowing. It keeps doing that, when it shows Harry it's snowing, and Mary it is not (or vice versa).
Continuity mistake: After leaving the diner, Lloyd & Harry are pulled over by a motorcyle cop (Harland Williams). As the cop notices the beer bottles on the floor of the van, you'll notice his hair has a curl hanging over his forehead. Right before he takes a drink of one of the bottles, the curl is gone. It cuts to Lloyd & Harry trying for a brief second , and when it cuts back to the cop saying "You'd shut your mouth if you knew what was good for ya," the curl is back.
Continuity mistake: When Jim Carrey and Jeff Daniels are in the restaurant, just before they encounter Seabass and right after they call the waitress "Flo", Jeff's coke glass is on his right side. The next shot shows it on his left, then his right, then his left again, without him touching it.
Continuity mistake: When Harry and Lloyd go to the preservation dinner, Nicholas is standing by the front door. A few minutes later, he is up on the stage starting the presentation and introducing Mr. Swanson. Then instantly, he is back by the front door talking to his comrade. There is no way Nicholas could have done what he did in so little time - he doesn't look out of breath -- and without being seen.
Visible crew/equipment: I think you can only see this in the DVD version, but when the guys are at the important benefit with the owls and Lloyd pops the cork off the wine bottle which kills one of the owls, in the part where you see behind the cork and it is spinning you can see the stick which holds it (the cork) up.
Factual error: Why don't the "beer" bottles on the floor of the van fall over? When the cop stops Harry and Lloyd the bottles are all standing perfectly upright and there has not been any spillage on the floor. Bear in mind that before this they had been driving on the verge and stopping and swaying when the cop tells them to pull over. And Harry is only holding 3, and yet 6 appear on the floor.