Corrected entry: When Boo is first discovered by Mike & Sully, they refer to Boo as 'it' and 'the child'. During the bathroom scene when Sully tells Mike that he named the child Boo, his exact words are "That's what I named her". There is no explanation why he switched the pronoun from 'it' to 'her'. For the rest of the movie, they do refer to Boo as 'her'.
Sangie
22nd Sep 2003
Correction: This isn't a mistake, it's a choice made by the filmmakers. It's intended to show that Sully no longer sees Boo as an "it", but as a living being that might not be so dangerous after all.
Phil C.