When Ben, Kate, Elliot and Joey are eating pasta, Ben has a cut above his right eye. When they switch back to Ben, there is a band-aid on the cut, and he had not left the table at all.
When George is playing the piano at the wedding reception, the sounds do not match up with what his hands are playing.
The notes the girl plays on the piano during her lesson do not match with the notes heard.
When George advises the young girl playing a Frédéric Chopin piece on the piano (supposedly without sufficient feeling), that she should let the music take her somewhere, surprise or even overwhelm her, he says that this is as important as "knowing the difference between a half-step and a semitone". Fact is, a half-step IS a semitone; there is no difference at all.