Goofs

During the rehearsal scene. A cigarette pack disappears from the podium as Harrison conducts.

Early in the movie, there's a discussion about the concertmaster having questions about fingering styles. There are no "styles" like French. The concertmaster of a professional orchestra would be the head of his/her section, and would set things like bowing. He/she might have questions about bowing, but definitely not fingering.

The "recording machine" Rex Harrison was trying to use in his fantasy was not a recording machine at all but a Garrard RC-100 flip-over 1938 record changer.

Just prior to the first murder-scenario fantasy, Sir Alfred's shadow is visible on the rear-screen projection screen as the camera tracks in on his eye.

Sir Alfred sets the detectives report on fire, throws it into the wastepaper basket, then stomps it out. He and the detective walk away, then realize the fire has set the drapes on fire. But there is no fire coming out of the wastepaper basket. Rather, the fire is only on the drapes, and that fire is coming from the floor initially, demonstrating that the source of the fire is NOT the wastepaper basket but something entirely different and outside of the wastepaper basket (some kind of pyrotechnic devise set off by a stage hand???).

Aroostook is said to be "in the neighborhood of Nova Scotia". Nearly the entire Canadian province of New Brunswick is between Aroostook and Nova Scotia.