Source(paywall): https://www.nytimes.com/2020/11/13/science/platypus-glow-ultraviolet.html From the post: >>When last we checked on the platypus, it was confounding our expectations of mammals with its webbed feet, duck-like bill and laying of eggs. More than that, it was producing venom. Now it turns out that even its drab-seeming coat has been hiding a secret — when you turn on the blacklights, it starts to glow. As noted last month in the journal Mammalia, shining an ultraviolet light on a platypus makes the animal’s fur fluoresce with a greenish-blue tint. They’re one of the few mammals known to exhibit this trait. And we’re still in the dark about why they do it — if there is a reason at all.