Continuity: When the dog is on fire, Pat gets a vase of water and pours it on the dog. In a wide shot the dog is on it's back, with all fours pointed up in the air. Yet in the closeup of the water being poured on the dog, the dog is on it's stomach just sitting down properly. This is obviously due to the switch of the fake dog to the real dog.

Continuity: When Mary has lunch with three friends, in a wide shot one of her friends picks up her drink and brings it to face level. In the following closeup of her, she brings the drink to her face again.

Continuity: The crowd that watches the guy fight with Warren and Ted near the beginning keeps on changing. People move where they're standing between shots and the arrangment of the crowd changes throughout the scene between shots too.

Continuity: In the scene where Ted is sitting on his bed, he pulls out his wallet to look at a picture of Mary. When he first pulls it out, he is looking at it from the side. But when they actually show you the face of the picture, it is upright.

Deliberate "mistake": The man kissing Cameron Diaz in that last shot (when the homeless guy shoots the drummer) is not Ben Stiller, noticeable by his much taller, slender figure.

Continuity: When Ted and Mary are sitting on top of the car, Mary looks at her watch to see what the time is, but if you look closely, her watch is facing the camera, so there is no way she could have seen what the time was.

Factual error: When Ben Stiller gets done "cleaning the pipes", he looks around the bathroom for "the missing hair gel", it is shown hanging from his ear when he answers the door. This is somewhat unrealistic. This glob of "hair gel" would never have hung onto his ear for as long as it did. It would have dripped onto his shoulder long before he reached the door.

Visible crew/equipment: Just before Warren's fishing hook gets stuck in Ted's lip, the camera pans from showing Warren fishing to Ted and Mary. Here you can see the reflection of the crew on the ground and finally on Ted and Mary when they are standing there.

Deliberate "mistake": When Ben Stiller gets done "cleaning the pipes", he looks around the bathroom for "the missing hair gel", he should have known where it was simply by his senses. Earlobes have feeling in them. He should have felt something wet on his earlobe. He also would have felt it dangling from his earlobe.

Continuity: In the scene at the fairground, Cameron Diaz is holding a stick of very abundant cotton candy. The camera pans away for a few seconds, and when it returns the cotton candy is almost completely finished.

Continuity: At the end of the film, when the camera is focused on all of Mary's suitors in her apartment, you clearly hear Matt Dillon say "Dom?!" off camera (as if he entered the room and was surprised to see Woogie there).  A few seconds later, he bursts through the door, sees Woogie and says "Dom?!".

Continuity: Ted makes fingernail marks in the floor when Puffy is pulling him along. Two things wrong: His fingernails aren't even touching the floor when he makes them, and the marks seem to disappear in almost all of the long shots.

Continuity: When Ted sees Mary for the first time in years, the hood on his sweatshirt changes from his back to his right shoulder.

Revealing: When the investigator takes Ted's head and starts slamming it on the table after Ted got finished telling them about the hitchhiker, Ted's head never hits the table but his own hand.

Continuity: Ben Stiller's character gets "hooked" with Warren's fishing line, getting a hook that quite noticeably has the prongs sticking out of his cheek when they are removing it. In the next scene, however, no scar, and no sign of the injury exists.