From Flanders: A Cultural History by Andre de Vries (page 96-97):

One of the world’s most unlikely episodes took place in Ghent: the filming of a version of Romeo and Juliet – acted entirely by cats. This 1970 oddity was the brainchild of Armando Acosta, a Spanish-American director and son of Hollywood scriptwriter Mercedes Acosta. Acosta Jr., who also runs a religious sect and has taken the name of Ganapati (after the Indian elephant god) after spending time in the 1960s following a Hindu guru, used his disciples to produce the film. The only human actor, meanwhile, was John Hurt, cast in the unlikely role of “La Dame aux Chats,” an eccentric boatwoman. (In an understatement Hurt later described it as “a fairly extraordinary film.”) The feline cast was voiced by actors, including Ben Kingsley, Quentin Crisp, Maggie Smith and Vanessa Redgrave.

Even without special effects, the cats put in a remarkably good performance, especially when at one point two hundred of them were released across the Sint-Michiels Bridge in the direction of the Belfry. They had been kept indoors for the winter to be trained as extras and half of them did not bother to return. According to the director’s wishes, the film can only be shown to the accompaniment of Prokofiev’s ballet Romeo and Juliet with a live symphony orchestra. After the release, there was a tour of world capitals, but the film has rarely been shown since.

IMDB says it’s a 1990 movie (typo in my book). Such a rare movie none of us can dream of seeing it. If your town’s orchestra will play along with it, let me know what it’s like.