Disagree with that being funny... sounds dangerous honestly. That dog could get hurt chewing on metal bits. My neighbor's dog ate a spark plug once and it was a whole thing.
Seriously though, people forget how much random metal junk ends up on the ground. It's not just obvious stuff, little bits break off things all the time.
Wait, a spark plug? How did that even happen, did the dog just find it in the garage or something? That sounds like a nightmare vet visit. Makes you wonder what other weird metal scraps are just lying around where pets can get them.