Lots of stuff frightens us that should frighten us – things that pose a clear threat to our physical wellbeing, for example. But what about things that just... creep us out? A shadowy visage, for example, or an almost – but still not quitehuman-looking robot?

In the latest installment of VSauce, Michael Stevens takes a fascinating look at the subtler qualities of "scary stuff," with a special emphasis on terror and creepiness – feelings he argues stem primarily from a sense of ambiguity:

Creepy things are kind of an ambiguity but they're also kind of not, so our brains don't know what to do. Some parts respond with fear, while other parts don't, and they don't know why. So instead of achieving a typical fear response – horror – we simply feel uneasy. Terror. Creeped out. Between the mountains of safety and danger there is a valley of creepiness, where the limits of our trust and knowledge and security aren't very clear.

Also known as the uncanny valley! It's a poorly understood phenomena, but what little research has been done on the subject is fascinating. Let Stevens be your guide.