Continuity mistake: In the opening sequence, Felix (Jack Lemmon) goes into the Metropole Cafe. One of the people he passes as he enters is a young woman with a thin face and very distinctive nose and eyes. He goes in, has a drink, hurts his neck, and leaves. As he is leaving, the camera pans the band and go-go dancers. One of the dancers is the young woman who had just left as he was entering.
Continuity mistake: At the baseball game Oscar is sitting and eating a hot dog, when the other guy answers the phone he is sitting there typing with no hot dog. When they cut back to Oscar he is sitting with the hot dog again.