I'm one of those freaks who sees the things that are wrong in movies, tv shows, etc. I don't try to do it, I just pick up on them for some reason. For example, in the movie Anaconda, when the boat is sitting in front of a waterfall look closely and you'll see the waterfall is flowing up instead of down. Somebody spliced the film in backwards.
Anyway, where Seinfeld's concerned (my wife and I are both huge fans) this is more of an "I'd like to know if they did it on purpose". In "The Dinner Party" (episode 77) Jerry and Elaine are at the bakery to pick up a gift. While waiting, Jerry has a black and white cookie. When he gets it, he takes a bite of half black and half white at the top. As the scenes change, the white and black sides flip. Sometimes the black is on the left and sometimes it's on the right. The problem is the cookie is only frosted on one side and the first bite is the only one taken, so it has to be two different cookies in the different scenes. Was it planned or just an oops?