My childhood cats hated their bells so much they learned how to abuse the breakaway safety clasps on their collars and get them off entirely. Sneaky indeed.

I think it might be a bell, but definitely some kind of collar accessory thing.

This is probably on the right track, but just wanted to add a little detail. Elastic deformation is when something fully springs back to its original shape. Plastic deformation has some spring back, but some portion of the deformation remains after the force is removed. Unless of course you bend it to the point of breaking. I’d imagine that means that in the brittle zone in the image there’s virtually no deformation, just force applied until a break occurs.