Ever wondered what happens when a fluid is both a liquid AND a gas at the same time? Steve Mould just fired up one of the rarest devices on Earth to show off the bizarre world of supercritical CO₂, the same stuff used to decaffeinate coffee.

Inside a transparent, pressure-proof chamber, CO2 shifts from solid to liquid to gas… and then into a strange in-between state where the boundary literally disappears. It’s science magic you can actually see, and yes, it explains exactly why your coffee can be decaf without tasting like sadness.