In The Cat and the Fiddle, the Violin maker, Stradivarius is trying to capture Rita the cat for the purposes of killing her and using her innards, otherwise known as catgut, to make the strings of his violins. It is also shown that he has a large number of cats in cages which he plans to use for the same purpose.
Although it was said that cat gut was used to make the strings of violins, this was actually a myth more than likely perpetuated by many a renowned violin maker during the 17th century and possibly earlier. The strings of a violin were actually made from sheep innards, which would have been fairly easy to come by. However, in order to protect their methods for successfully making a stringed violin, the rumor that cat gut was integral to the manufacture of a quality violin came to be accepted as fact, and not fiction.
Superstition held that it was incredibly unlucky to kill a cat, so whoever perpetuated the myth knew that superstition would thereby prevent competitors.
"Catgut" is prepared from the natural fibre found in the walls of animal intestines like sheep or cattle in addition to a few others. However despite its name, "catgut" manufacturers do not use actual cat intestines.