Catgut is a tough, stretchy cord made from the intestines of sheep, goats, or other animals (despite the name, it's rarely made from cats). For centuries, this natural material has been twisted and dried into strong strings used for musical instruments, tennis rackets, and surgical stitches.

When you hear a violin, cello, or acoustic guitar, you might be hearing catgut strings vibrating to create sound. Musicians valued catgut because it produces a warm, rich tone that many people prefer over modern synthetic strings. The material is also incredibly strong for its thinness: a catgut tennis racket string from the early 1900s could withstand the impact of a speeding ball thousands of times.

Surgeons once used catgut stitches inside the body because, unlike regular thread, catgut would naturally dissolve as wounds healed, so doctors didn't need to remove them. Today, most musicians use synthetic strings and surgeons use laboratory-made materials, but some traditional instrument makers still prefer real catgut for its unique sound.