I had a cat that used to eat thread, it's dangerous because it can get tangled up in their intestines. The first time I caught my cat, I had to rush him to the vet for emergency surgery. Sadly a year later he got hold of some thread and we lost him, I didn't realize until it was too late. Some cats seem to have a fetish for thread, my cat I have now likes to lay on my sewing table sleeping while I sew, every so often he wakes up and checks out what I'm making then goes back to sleep.... :)