This is no optical illusion – the water droplets you see here are actually rolling uphill. But how?
What you're looking at is a unique demonstration of the ever-fascinating Leidenfrost effect. Named after 18th Century German doctor Johann Gottlob Leidenfrost, the phenomenon occurs when liquid comes into contact with a surface that is much, much hotter than the liquid's boiling point. Under such conditions, an insulating layer of vapor is created between the droplet and the surface. In the case of a water on, say, a piping hot frying pan, the water droplet can actually float on the layer of vapor. This not only causes the droplet to hover, it also protects the water from boiling outright.