Exposing ANY part of your body to a cryogen is a risky thing to do, I posted the above not to suggest it is 'safe', I was just pointing out that it could be done without injury by those familiar with LN2 and its properties and behavior.

If not done exactly right the demonstration I wrote about WILL result in serious injury as Nick said... In other words- 'kids dont try this at home!'

Using a metal object instead of a rubber eraser would likely result in injury... leaving your hand in a split second too long could lead to injury (I never tried to push the duration to find out how long was 'safe'). Splashing from the boiling LN2 could lead to the liquid being trapped against your skin by your clothes resulting in injury.