When George sells his ticket to the heavy set Asian man, 'Harry Fong', outside the opera as Susan arrives, they say they agreed on $250 for the ticket. Inside the theater, 'Harry' sits down next to Jerry who asks him what he paid for his ticket, and he says $175.
When George and Jerry are about to leave for the opera, the tips on Jerry's tuxedo collar go from on top of his bow tie to behind the tie.
When Jerry (Jerry Seinfeld) tells Elaine (Julia Louis-Dreyfus) that he's looking forward to meeting her new boyfriend, a jar of pickles appears on the counter suddenly.
The cast continually refer to the character in the opera as 'Pagliacci'. This is the Italian plural form, which is the name of the opera, but a singular clown is 'pagliaccio'
When Joe Davola (Peter Crombie) leaves his message on Jerry's (Jerry Seinfeld) answering machine, he sputters four times due to the hair on his tongue. Later, when Jerry listens to it we only hear Joe sputter three times.