Don’t worry, it’s not a real mouse. Heaven forbid. It’s just one of those toy mice that eventually gets stripped down to its bare plastic shape. Our cats have one like that.
This is a very special kitten–more interested in the toy itself than in the bag it came in. It’s my experience that nothing beats a cardboard box… although our girl Missy thought nothing beat a fresh pipe cleaner. She’d play “fetch” with those.