Trivia: When Claudin thinks his concerto has been stolen, he goes into a frenzy and attacks the music publisher. The publisher's assistant, Georgette, stops the attack by splashing a tray full of powerful etching acid into Claudin's face. Oddly, Claudin does not recoil when she throws the acid; rather, he leans forward, as if to ensure that it the liquid strikes him full in the face. Which is precisely what happened. To avoid having to shoot the messy scene more than once, we see actor Claude Rains deliberately leaning into the splash for a thorough dousing.
Trivia: Hitchcock's cameo comes relatively early in the film - he is playing bridge with a man and a woman on the train to Santa Rosa.