As an ailurophile I would protest vehemently the usage of a cat's innards for the use of strings for tennis rackets. I can't think of a valid reason I shouldn't also protest the use of sheep intestines either. According to my source, cats have never been used for this--consider catgut, sheepgut.
After washing, cutting into ribbons, and scraping away muscle tissue, the ribbons of the lamb's intestines are soaked in an alkaline bath for several hours. Then they stretch them into frames and later remove them while still moist to be organized by size, then twisted into cords.
These days, catgut usage is being usurped by the evil forces of nylon and steel when making tennis rackets, though violin, cello, and guitar strings still use the butchered intestines of the great wooly mammals, and in particular these days the Pirazzi family have the ripest flock in Offenbach, Germany. They make strings for Paganini.
Repeat after me: About 50 percent of all suturing is done with catgut. Yes, folks, you are probably walking around stale sheep guts tying your broken bodies. It is slowly absorbed by the body. It is likely you have eaten catgut. It's a tasty treat for all ages. It is used as the casings of sausages. And that's all about catgut.
How do they do that? by Caroline Sutton. 1981