Other mistake: When the film starts, Dolittle drinks from a yellow cup, the angle changes to behind his shoulder and it's perfectly obvious the cup is empty. Then, despite this, he keeps sipping and moving his mouth all the time.
Other mistake: When all the animals visit Dolittle at his apartment and he turns on the light in the hallway, you hear a click and the lights turn on, but there is no light switch.
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.