Revealing mistake: When Cindy and Buddy get trapped inside the cold chamber, she starts rubbing him to a point that it becomes masturbation. But when she's sitting on his legs doing the thing, in one side shot you can clearly see she is not holding his privates and her hand is just going up and down, closed but empty.
Continuity mistake: When the butler is serving up the turkey, he holds up a plate full of what looks like turkey, salad and mash. When he puts it on the table, the plate just has turkey on it.
Revealing mistake: In the wheelchair duel, you can see that Dwight is "burning rubber" with his wheelchair, but the wheels are not moving.
Revealing mistake: When the guy with the weird hand is serving dinner, you can clealy see through the cuff on his left arm that his real hand is there.
Visible crew/equipment: At the end of the film when the bird is pooing on the wall, you can clearly see the pipe leading up to the fake bird which is making it do this.
Continuity mistake: When the two guys are facing off in their wheelchairs the doves fly by and poop on the bald guy's head. But as he starts to move the poop is gone. But in the next shot it's back again.
Continuity mistake: After the man in the wheelchair first breaks his glasses. It is then in perfect shape in one scene, then broken again in another scene. This continues on for a few minutes.
Continuity mistake: About Dwight, the guy in a wheel chair, and his hair. In the scene where he fights the ghost, they change all the time. It starts out as a mess. And then it's in a pony tail. It keeps changing throughout the whole struggling scene.
Revealing mistake: When the couple split the pole, they get hit by a bus. As the shot cuts to a wide shot, and if you pause in the right place, you can see the couple have been replaced by dummies, just before the bus hits them. [This isn't a "mistake" -- this is just dissecting a movie, frame by frame, until you can spot the special effects.]
Continuity mistake: In the scene of the dinner, Hanson cuts the turkey, but in a scene when Dwight is speaking, the turkey is perfectly OK.
Continuity mistake: When Dwight is handing everybody goggles, cup walkie talkies etc., the red numbers on the machine nearby keep changing in most shots. You can clearly see "02.38.58" and it is counting down. Then in the next shot it is "02.39.48" and is counting up. Then it is "02.17.00" etc.