When you go out with a metal detector, I assume there are plenty of things you're hoping to find. Things of value... ya know, like jewelry. Maybe you'll find some pieces of old buildings or something.
Ever think you'd find a cannonball from the Civil War?
A couple of VA kids found one, but had no idea [even though it looks like a Pokeball]... carried it home and proudly presented it like they're cats with a mouse. Then the cops had to be called, who then called other authorities to "dispose of it properly" by blowing it up somewhere else.