What does the platypus's stinger do?

Oh, dude, the platypus's stinger is actually not a stinger at all. It's more like a spur located on the hind legs of males that can deliver venom. So, it's not really for stinging like a bee or a scorpion, but more for defending territory and competing with other males. It's like nature's way of saying, "Back off, bro."