Filmed early April 1939, released November in Britain, March 1940 in US. Bela Lugosi shot this feature after "The Gorilla" and before "The Phantom Creeps".
Holt's statement "As the walrus said to the carpenter, the time has come..." is a reference to the poem, 'The Walrus and the Carpenter', from Lewis Carroll's 'Through the Looking-Glass and What Alice Found There'.
Orloff's quote "And the greatest of these is Charity..." is from 1st Corinthians 13:13.
The first film in Britain to receive the 'H' (for Horror) certificate.
The Stainsbury machine is a Braille shorthand machine. Henry Stainsby, superintendent of Birmingham Institution of the Blind in England and Alfred Wayne developed several of these devices, commencing in 1899. The one seen on the film is similar to the 'Improved Stainsby Braille Writer' of 1933.