Continuity mistake: When Greg goes into Denny's room to get clothes, Denny sneaks back home and the chair is by the window facing backwards, one shot later the chair is facing the other direction.
Continuity mistake: When Greg is eating dinner with Pam's parents, his amount of sweet potatoes on his plate varies, sometimes there's many on his plate, other times there are less. (00:30:30)
Continuity mistake: Jack watches a tape of Greg in which Greg mentions Denny and hints at Denny's drug use. However, the tape is of Greg's first (and only) night at the house. Greg didn't meet Denny until his second day at the house.
Continuity mistake: When Greg and Pam are dancing in the restaurant, just before De Niro picks up the message from the neighbour about the cat, when the shot is on Greg's face their heads are together, but when the shot is on Pam's face, their heads are separated. This is shown like 8 times, 4 times each side.
Continuity mistake: When Greg is on the plane at the end fighting with the stewardess, her collar goes from being tucked in, to untucked several times.
Continuity mistake: In the race scene on the way home when Greg is driving the car you can see in the background that the seat belt keeps switching positions. Sometimes it is around Bob then it is around Bob and Debbie.
Continuity mistake: When Jack is talking to Greg in the airport luggage room after he is thrown off the plane, the glow on the table from the light keeps changing shape, from round to square.
Continuity mistake: In a few scenes of Pam's bedroom, if you were standing at the foot of her bed and look to the right you would notice that there isn't a night stand nor a lamp sitting on it. So how is it that Greg happens to turn on a lamp that is sitting on a night stand when he proposes to her?
Continuity mistake: When Greg and Pam's Dad are on their way to the store and they're in the car, Pam's dad is moving the wheel every way when you can see that the car is going straight and finally when they make a turn the wheel is straight.
Continuity mistake: When Jack and Greg are racing home after the rehearsal dinner, they screech at the same intersection, (by Dunkin Donuts) numerous times. You can see several sets of skid marks already on the road. (01:19:45)
Continuity mistake: In the den, when Pam is telling Greg how much she loves him, she has her arms around his neck. From over her shoulder, it appears that her arms are under the hood of Greg's shirt, but from over Greg's shoulder, her arms are on top of the hood.
Continuity mistake: In the beginning of the film, when De Niro is holding the cat explaining to Pam and Greg how he taught the cat to use the bathroom, the cat changes from shot to shot. In some shots it's a very fluffy Himalayan with a lot of black on its head, then the next shot it's a much less fluffy cat with more gray on its head. The positioning of the cat in De Niro's arms also changes from shot to shot in this scene.
Continuity mistake: When they sit down at the dinner table on the first night, Jack reads the poem he wrote about his mother. He is not wearing reading glasses, but when the shot moves away and returns, Jack is now wearing reading glasses.
Continuity mistake: When Pam goes into the den to console Greg after firing the 'shot heard round the world,' she puts her arms around his neck. In alternating shots, her hands go from under the hood of his sweatshirt to on top of the hood.
Continuity mistake: Before the fire scene, the rain gutter is on fire in several places. But when the rain gutter gets disconnected, the fire in the rest of the rain gutter mysteriously disappears.
Continuity mistake: In the 'race scene' near the end of the film, just before Greg and Jack go their separate ways, you see Larry (who is sitting next to Greg) say, 'Oh, look, there's Jack. Hey, Jackie,' and he waves. Then it cuts to Jack, who is looking at Greg, and then it goes back to Greg, and in the background you see Larry and he is unfolding a newspaper and starts reading it. Then it goes back to Jack, and then back to Greg, where you see Larry with his hands on the dashboard, looking at Jack. So what was with the newspaper? Where did it come from? How did it disappear so quickly?
Continuity mistake: During the scene when everyone is gathered around discussing the whereabouts of Mr. Jinx, Jack announces "We'll just have to reschedule..." Debbie jumps up from the couch and when she does she hits the coffee table causing one of the edges of the table to fall and hit Denny's knee. The next shot the edge is back in place off Denny's knee and Denny has slightly changed positions.
Continuity mistake: Before and throughout the scene where Jack demonstrates his hidden cameras, the lemon and cherry in Greg's glass keep moving around.
Continuity mistake: When Greg is trying to open the suitcase, the top pouch is empty, when the delivery man drops it off, and when Jack tries to open it, the top pouch is full.