document: 15 May 2017 Last updated at 13:14 BST
  The narwhal is a mysterious member of the whale family that mostly lives in the Arctic.
  It has a long pointy tusk that points out of the end of its nose - that's led to the creature having the nickname, the "unicorn whale".
  Scientist knew very little about what these tusks were for until they started filming them in the wild, using drones.
  Now they know it's part of a clever way to hunt fish...
  Watch this...
summary: Scientists reckon they've figured out why the narwhal has its famous tusk.