What is this thing?

See pics, found this thing well healed in my cat's tail. Came out with no resistance and no bleeding. Looks like a tip to something, but not sure. Cat is less than 6 months old. Thoughts? The grooves you see are from my pliers. It's hollow and seems to be aluminum or some other soft metal.

Edit:

Looks like this is pretty unanimously solved. Bit of backstory (not that you asked)- neighbor got got 2 kittens in May/June for his daughter. They're freaking adorable so whenever they wandered over to our house, we gave them lots of attention. They had been spending more and more time camped out on our porch furniture in the past month and then I found this just today. I'm going to talk to the guy and see what's up.

I'm concerned they are only interested in animals while they're small and cute because last year they had a young dog that's no longer there, this is the second pair of kittens they've had this year (one of the first pair I still see sulking around at night, but I'm pretty sure it's feral now. No idea what happened to number 2), and now they have a new puppy again.

Thanks all!

Minor second edit: I made a mistake about their pets. The first dog mentioned above was actually the house next to the neighbors in question. Those neighbors had moved, which is why the dog is no longer here.