Spooks Run Wild (1941)
Lugosi character dresses like Dracula and is suspected of being a vampire (though the word "vampire" is never used)
Slip and Sach reuse the 'how do you read in the dark?' 'I went to night school' joke from this movie
mentioned by the host Jakob Stegelmann
A poster for the film is visible in one of the scenes.
footage used in episode