Continuity mistake: At the beginning of the movie, Harry's van has bucket seats, yet later on when the "gas-man" rides along, he is sitting on a bench seat in-between Harry and Lloyd. (00:38:00)
Suggested correction: Mental isn't sitting on a bench seat, it's implied he's sitting on the floor of the van in between the both of them. Although hard to see, the backs of the bucket seats can still be seen behind Harry and Lloyd at certain points. You see a fair bit of it behind Harry whilst he's dancing as Lloyd sings the line "and if that mocking bird don't sing".
Continuity mistake: When Lloyd drops Mary off at the airport, the interior of the car is different once Lloyd gets back in.
Suggested correction: The interior is the same, but looks different due to the direct sunlight in the first shot (blue instead of black). The only difference is the steering wheel, which is not contain the airbag on the way to the airport, but is totally different when Lloyd is back in the car and is driving right before the impact.
Revealing mistake: During the tongue scene, when Mary is pulling Harry's tongue off the ski lift, you can see Harry's real tongue right under the fake stretchy one. (01:16:50)
Suggested correction: If you look really carefully you will see that this is a part of his lower lip folded a little bit.
Continuity mistake: When Lloyd is peeing in the beer bottles, he hands them to Harry... it shows him holding the bottles... next shot, he isn't holding them, and the shot after that, he is holding them again. (00:26:00)
Suggested correction: In the shot where he is "not holding them", they are simply out of the frame. He was actually holding them all along.
Plot hole: By the time Lloyd gets to the airbridge the plane had already left. The finalisation of the boarding process after last call, plus push back takes at least 15 minutes. Lloyd would have easily caught up to Mary or the plane would have still been there.
Plot hole: After Lloyd's encounter with Seabass in the restroom at the gas station, we see the FBI waiting for Harry and Lloyd at the Colorado border (we even see a front shot of the road and mileage sign), and there is no town in sight. Then we see Harry and Lloyd 3 miles from the border, driving toward it, where the FBI are waiting. Then we see Lloyd coming out of a market in a little town, after which, upon leaving the town, he drives in the wrong direction. How did they suddenly come upon this little town, especially when they were only 3 miles from the border? Did they turn around, or what happened? (In the unrated version, the van scene 3 miles from the border is extended, and it seems that they would have reached the border, and the FBI, by now.) The whole scene here is pretty confusing.
Suggested correction: Why couldn't this little town be inside those 3 miles? They stop there right after they talk, Lloyd made the wrong turn, maybe, 200 yards from the cops on the border, and they didn't see him at night... What's wrong?
Continuity mistake: Lloyd reads the article about Mary and can't even pronounce the word "the", yet when Harry says look on the briefcase for her name, he says "Samsonite" with no problems, and Lloyd can easily read the "Man Walks On The Moon" newspaper headline in the hotel bar.
Suggested correction: That isn't a continuity mistake - it is meant to be funny or ironic... or part of the "dumbness." Humor is often comprised of violations of expectations. He can read a big word like "Samsonite" but not a three-letter word like "the." (Less likely, it is also plausible that he didn't actually read the word "Samsonite" but recognized it as a name-brand symbol).
