Deliberate mistake: At the end of the movie when everyone is on the bridge, the one female cop roundhouses the bad guy, who is clearly a white male in his 50's, but his stunt double is an Asian man (with different colored hair). They use the same stunt man a few other times for people he doesn't even look like.
Deliberate mistake: In the first bowling scene, all the lane numbers are backwards.
Deliberate mistake: During the movie, when Mulan is just a girl, you can see that her eyelashes extend beyond her eyes. When she is pretending to be a boy, her eyelashes are short (this makes perfect sense). But when she is in the medical tent her eyelashes are long even though she had no time to put on makeup. This is deliberate though, because without it she would have still looked like a boy, and just pulling her hair down wouldn't make her look any different (since that's how she looked in the pond). So they had to change her eyelashes to make her look more girlish.
Deliberate mistake: When Tiff (as a doll) lights her Zippo you don't see her clicking the flint, even though one can hear a 'clicking' sound. (00:33:35)
Deliberate mistake: In the scene where Maya is looking for Rodney at the party and he scampers off into the bathroom, he miraculously climbs on top of a toilet in a matter of seconds (which isn't actually shown). There is no way a guinea pig could do this.
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. (01:52:40)
Deliberate mistake: In the funeral scene, Ned Devine himself (i.e. the actor who played his dead body) is one of the extras sitting in the back row.
Deliberate mistake: During Alejandro and Elena's duel, he slashes her skirt and reveals her bare leg. When he slashes off her whole gown, she's somehow wearing leggings. Obviously so Catherine Zeta-Jones would not be naked.
Deliberate mistake: While Laurence is driving to the park trying to find Martha there are closeups of his car en route, and one of the closeups of the front left side of his car is a flipped shot, note the backwards "Saab" and the surface damage which is actually at the right side of his car. (00:56:00)