Hot water can freeze faster than cold water.
As impossible as it sounds, this one is actually true. It's called The Mpemba Effect, named after Erasto Mpemba when he noticed it in 1963. Amazingly though, it was actually discovered long before that...by Aristotle. Nobody knows exactly why this happens but the most plausible theory is that boiling the water removes some of the substances dissolved in it which makes it easier to freeze.
This works in reverse when salt is put on the ground on cold days to melt the ice. In this instance, the salt dissolves, making freezing more difficult. For more information, check out this video by VSauce