Does tapping a drink can to stop it exploding work?

It does certainly have an effect. Or it can have an effect. I haven't got it to work 100% but it's supposed to help. The idea is that if you have shaken up a can, the reason why it explodes is there's lots of little bubbles of carbon dioxide in the liquid already. That gives the dissolved gas lots of nucleation sites - places to start bubbles, and they can get bigger very, very quickly. Because these bubbles start under the liquid, it all explodes and forms a foam. If you tap it, the idea is you dislodge the ones which are stuck around the bottom and along the sides to get fewer bubbles in there at the bottom, so it makes the foam much more slowly and it doesn't make a mess.