Reportedly Universal Studios executives were displeased when they viewed the first cut of 'The Black Cat' (1934) and so ordered the director to do some extra shooting to tone the violence and horror down. Edgar G. Ulmer did the opposite, and added in the now-famous sequence where Poelzig (Boris Karloff) views his dead but preserved wives before he reveals the fate of Karen to Dr. Werdegast.
Censors in Italy, Finland and Austria banned the movie outright, while others required cuts of the more gruesome sequences.
The film was the first collaboration of Bela Lugosi and Boris Karloff, who at the time were unquestionably the two biggest stars of horror film. Despite rumors that the two stars were personally very competitive, this marked the beginning of a pleasant working relationship between the two. While Lugosi and Karloff never became close personal friends, they were quite amicable to each other and enjoyed working together. - IMDB
"Poor old Bela, it was a strange thing. He was really a shy, sensitive, talented man who had a fine career on the classical stage in Europe, but he made a fatal mistake. He never took the trouble to learn our language. He had real problems with his speech and difficulty interpreting lines." - Boris Karloff