Your body produces more than a liter of mucus every day, and when you’re sick, it can be hard to miss. But what exactly is mucus? And what does it do, besides making you miserable? Katharina Ribbeck reveals the mysteries of this transparent, shape-shifting layer that moistens and lubricates the vulnerable parts of our body while rendering us invisible to potentially deadly microbes.

Lesson by Katharina Ribbeck, animation by Anton Bogaty.