According to Roger Ebert in his Movie Answerman Column, when he and Gene Siskel are talking to each other during the opening of the show as they are walking into the theater, Roger is saying to Gene "That was a good review" and Gene is saying to Roger "I wish I'd read your review before I saw the film."
One of the most infamous episodes of the show when Roger Ebert gave thumbs down to Blue Velvet (1986), a critically acclaimed film at the time and later on.