You draw the outline of your left hand on a sheet of paper.
A spectator takes a lit match (or cigarette) and freely selects to burn any fingertip.
Once he's done so, and you've made proper facial expressions and groans of pain, YOU then show him
that the fingertip on your actual left hand that corresponds with the fingertip he burned has a large blister.
Nothing is added to your finger. The blister looks real. No pain is involved.