If you’ve ever shakily stepped onto the ice at your local skating rink, you are intimately familiar with the fear of falling on slippery ice. But what makes ice so slippery in the first place? Interestingly enough, scientists are still trying to figure that one out.

Physicists used to believe that ice became slippery when it was exposed to applied pressure. This pressure, they theorized, lowered the melting temperature of the top layer of ice. They believed that when a person went ice skating, the pressure from the blade caused the topmost layer of ice to melt. The thin layer of water allowed the ice skate to glide easily over the surface. After the blade passed, the top layer of water refroze.

However, most scientists today claim that this theory is wrong. “Ice is a very mysterious solid,” Robert M. Rosenberg, a chemistry professor at Lawrence University, said in an interview with The New York Times.

Scientists found that while pressure does lower the melting point of ice, it only does so by a fraction of a degree. Instead, they proposed that the friction from an ice skate causes the ice to melt beneath it.

Others believe that ice naturally possesses a fluid layer comprised of unstable water molecules. While these molecules search for stability, they move chaotically over the ice’s surface and create a slippery layer.