Revealing mistake: When Dolittle is called in the middle of the night to give Miss Parker her injection, watch the injection: When Dolittle pulls the injection equipment away from her fat leg, the needle is gone.
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.
Revealing mistake: Dolittle's daughter is in the woods holding the cell phone talking with his dad about the dog he is bringing, but the phone screen is off all the time.
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.