Gustavo Sereno and Gee Magic together are sharing with the magic community a revolutionary blister effect that will allow you to amaze your audience. They will remember you for the rest of their lives.
You introduce an envelope by saying that inside there is a prediction. Then you ask your spectators to think of any playing card (no force at all) and name it. You open the envelope and you drop a lighter into the spectator's hands. The lighter is ignited, and you thrust your thumbs into the flame like you are burning yourself. You turn your thumbs towards the spectators and the skin has blistered in the shape of the freely named card's suit and number!
If you don't like to use playing cards, you can perform the number version. You ask the spectators to think of any number from 1 to 100 and name it. Your thumbs will be blistered with the thought-of number.