I like to think I made it exciting.... We had one lab that used liquid nitrogen, all the 'kids' thought it was cool (no pun intended) I let them drop all sorts of things in the liquid nitrogen to freeze them- a piece of bannana, a bit of rubber hose, etc.... finally one student wanted to freeze their rubber eraser, we dropped it in and the liquid nitrogen bubbled and then became still as the eraser became the same temperature- I set aside the tongs that I had been using to fish out the previous things we had frozen, and plunged my bare hand into the liquid nitrogen to pick up the eraser- There were screams from the students, both male and female, I picked up the eraser (rolling it in my hand so it didnt freeze my skin) and threw it down- it shattered like glass.... I then lectured about the Leidenfrost (sp?) effect, I was perfectly safe putting my bare hand in liquid nitrogen for a split second- the liquid boils away so fast that it never touches your skin, there is only a cold gas on your skin, and its harmless if you are only in contact with it for a second....

I found that my students were far more attentive after that demonstration....

I did another demonstration in a similar vein the next season.... that got me trouble, but it was funny as hell....