Actually, the pencil sharpener could give a louder squeaking noise than the grinding noise, that wouldn't be heard. Mine does, because the crank handle is not lubricated, and thereby emits a high pitched squeak which drowns out the grinding sound.
At the end of the movie, when it is explaining what each character is up to now, the text says that Charles Allen II is "writing a book on prison workout regimes." Some people regard this as a mistake and think the word should be "regimens". However, all major dictionaries recognize the use of "regime" to mean "regimen".