Factual error: There are a few things wrong with the swan egg that Maya has found. First, in the opening scene we see that the egg is a hard-shelled egg, and it appears much too large for a swan egg. Second, at the end of the film, the egg hatches to reveal a baby alligator. Alligator eggs are soft shelled. Third, alligators are not native to San Francisco, but the southeastern United States.
Continuity mistake: When Dolittle is a boy and his father sends the dog away, they show him crying, a single tear is coming down the right side of his face. The scene then shifts to the dog and back to young Dolittle. The single tear is now on the left side of his face.
Factual error: There is a scene in which the tiger gets out of the back of the jeep, but the suspension is not altered on its departure.
Continuity mistake: In the scene when John is talking to the vet about Lucky, watch the vet's hand on Lucky's tail. It moves from the base in one shot to the middle in another. This happens several times. Also, the tail changes length and fur color.
Revealing mistake: When John is preparing to operate on the tiger you can see a crowd of people watching including his family. Watch the guinea pig that his daughter Maya is holding - if you look closely at it you can see that it is fake.
Continuity mistake: When Lucky the dog is in Dolittle's car, he says "Tree, tree, tree" and in doing so, puts his paw on the button and gets his head stuck in the window. At this point you can see there is nothing next to Lucky's head, but in the very next shot he has placed his left paw on the window.