We don’t want to put you off reading this issue’s special feature, but sometimes the coolest and most compelling science can come from the most disgusting things. Take the slime in the image above, for example. That’s hagfish snot, produced as a defence mechanism in huge quantities by this deep sea-dweller. Just a teaspoon of hagfish mucus reacts with seawater to form a mug full of slime, and scientists are studying the stuff to better understand its properties for a range of useful things. We’ve delved into 40 facts about the world that are just as gross and also fascinating. You can read about them on page 20. Enjoy the issue!