Although Edward Chapman played the father of John Laurie and Kathleen O'Regan, he was four years younger than Laurie and two years older than O'Regan in real life.
Hitchcock's first film shot entirely with sound throughout. His previous film Blackmail was shot silently and later parts were re-filmed with sound, post dubbing being a non-existent technology yet, and released as a "part-talkie".
Sean O'Casey and Sir Alfred Hitchcock had formed a friendship prior to the filming. Hitchcock had a huge admiration for the original play and later said that he made the film (one of his most untypical) mainly because he didn't want anyone else to make it - he was fearful that an ordinary hack director would mess up the original and make a banal travesty of it. The friendship of the two men continued until Hitchcock left Britain in 1939. They never saw each other again after that, but Hitchcock remained fond of O'Casey and claimed that the Karl Swenson character in "The Birds" was a little homage to his friend.