Liquid nitrogen is famously one of the world's coldest substances, freezing and shattering anything it comes into contact with. But if you know what you're doing, you can safely stick your hand in it - as one brave blogger demonstrated.
Of course, before we get to the awesome footage of Popular Science blogger Theodore Grey actually putting his hand in liquid nitrogen, we should point out that this is definitely an experiment that you should not attempt at home. As he points out, the secret to pulling this off only works for less than a second, and it won't work at all if liquid nitrogen comes into contact with your clothes. So with those disclaimers out of the way, how is he doing it?
As Grey explains, he's protected by the Leidenfrost Effect, in which a liquid that comes into contact with something much hotter than itself forms an insulating layer of vapor to prevent the liquid from immediately boiling. (You can read all about the Leidenfrost Effect in our primer on the subject.) This vapor layer provided short-term protection for his hand against the dangerously cold liquid nitrogen, allowing him to safely place his hand in the liquid nitrogen again and again - although only for a split-second each time.
You can see a video of his awesomely foolhardy demonstration of the Leidenfrost Effect below. As he points out at the end of his post, the Leidenfrost Effect could also theoretically protect a person's hand from molten lead. He decided not to put that particular theory to the test, leaving the door open to other brave science bloggers to try the experiments themselves. Yeah...I think I'm just going to leave that door wide open, thanks.