Catgut is not made from cats! The term "catgut" is a misnomer.
Catgut is actually made from the intestines of sheep, goats, or sometimes horses. It has been used for centuries to make strings for musical instruments, surgical sutures, and other items.
The name likely comes from the past use of cat intestines for similar string, but this is no longer common. "Catgut" has become a general term for string made from animal intestines.