There are some movies we can't help but watch over and over, and one of those is Ferris Bueller's Day Off.But endlessly rewatching the classic comedy has taught us a lot.Thanks to Ferris, we all know how to fake being sick, we can recognize pointillism, and we know what a Von Steuben Day parade is. Still, no matter how many times you've watched the movie, there are some blink-and-you'll-miss-them details that speed right past you.Here are 10 you probably never noticed:1. Ferris has three siblingsParamount PicturesNotice anything strange about the family portrait on Mr. Bueller's desk?