Banned in China: Banned in Quebec - because the film featured scenes of infidelity that Samuel Goldwyn refused to cut.
California Doubling: Although they did actually import real heather from England to make it look more like Yorkshire. According to David Niven's autobiography, the heather took to the warm Californian sun and tripled in size - requiring filmmakers to cut it back before shooting.
Enforced Method Acting: Merle Oberon's distress when Cathy runs out into the storm looking for Heathcliff was quite real; she had to do take after take running into propeller driven water and eventually got hospitalised with a fever.
Focus Group Ending: The film was originally going to end with a shot of Heathcliff's corpse in the snow, but at producer Samuel Goldwyn's insistence, this ending was replaced with a romantic shot of Heathcliff and Cathy's spirits wandering the moors, Together in Death. By the time the new ending was filmed, Laurence Olivier and Merle Oberon had both moved on to other projects, so stand-ins took their place, which explains why the two ghosts are only seen from behind. Director William Wyler allegedly hated the new ending, but almost every subsequent film and TV adaptation of the book has ended in a similar way.
Merle Oberon and Laurence Olivier clashed repeatedly - since both were miserable at having to leave their loved ones at home in the UK. Laurence Olivier wasn't too fond of William Wyler's direction either, but later admitted that he helped him understand the difference between acting for film and stage.
Merle Oberon had a more mild version with David Niven. The two had been involved briefly for about a year not long beforehand - so working together was uncomfortable.
Never Work with Children or Animals: For the barnyard scenes, it was feared that the ducks and geese would make too much noise - so the animal trainer actually snipped their vocal cords.
Pop Culture Urban Legends: Rumors abound that the time period was moved forward to allow a short-of-funds William Wyler to reuse costumes from a Civil War drama. Others claim the time period was changed simply because Samuel Goldwyn thought the fashions were more attractive than Regency Era ones.
Troubled Production: Pretty much no one was happy with director William Wyler and his fondness for numerous takes (David Niven's first scene had about forty). So many of the actors clashed with each other - Laurence Olivier and Merle Oberon got into a shouting match over him accidentally spitting on her. Both of them also had foot injuries throughout filming, requiring them to hobble during their scenes. As mentioned above, Merle was hospitalized with a fever briefly due to the excessive takes of the storm scene. By the end of filming, it was thirteen days over schedule and $100,000 over budget.
Vivien Leigh really wanted to play Catherine alongside her husband Laurence Olivier. As she was then-unknown in Hollywood, they went with the original choice Merle Oberon. Vivien was offered the part of Isabella, but she turned that down.
Ronald Coleman, Douglas Fairbanks Jr and Robert Newton were considered for the role of Heathcliff before Laurence Olivier was finally cast.