Unless you've never seen the sea, you've probably seen a jellyfish. And even if you haven't seen one, you will almost certainly know what they look like. Despite this, scientists know surprisingly little about them. Which is why British and Irish researchers are in the middle of a project to tag them to find out things like where they go during the winter, how long they live and why they congregate around our coasts during the summer months. Sue Nelson goes to Swansea to find out more. Later, we learn something about water most of us had no idea about. Richard Hollingham goes to Leeds to talk to a researcher about supercooled water and discovers why you wouldn't want it in your aeroplane's fuel system.