Redditor parsect runs a metal-detecting service. As a new daycare center was about to open, he was asked to check the bark-chip playground mulch for anything that might be dangerous to children. He found quite a bit, as you see. What have we learned here? Never trust a construction crew to clean up all their mess, and get your kids vaccinated for tetanus.
The comments at reddit became a mini-AMA where parsect answered questions about his work. While he does find occasional jewelry, the weirdest thing was a stash of gellignite. He even showed us pictures.