Trivia: Eddie Murphy had a big problem while working on this movie: He is very squeamish about most animals. It is even so serious that he flatly refused to do a scene involving an alligator. Hence, most shots with animals were done via blue-screen technique.
Trivia: The scene where Dr Dolittle awakes to find the guinea pig in the bed with him looks like an homage to the horse's head scene in The Godfather. The way he screams, and the way the camera cuts to an external shot, is an exact copy.
Trivia: In the background at the circus, a two-headed llama can briefly be seen walking around. This is a reference to the original Dr. Dolittle story, which featured a two-headed llama called the "Pushmi-Pullyu."
Trivia: Archer Dolittle's name is never spoken in the film. It is only mentioned in the end credits.
Answer: Geno deliberately broke Mark's nose during the party after Mark made a snide remark. After the party, when Mark suggested a way to have John committed and still get their money, Geno had enough of Mark's ignorance and punched him in the nose again to add further insult to injury.