1. In a hurry, approach the top landing of a staircase.
2. Also in a hurry, notice that there is an empty garbage can waiting to be taken back downstairs.
3. Swoop down with your right hand to pick up the garbage can, removing your eyes from the staircase and therefore altering your initial trajectory.
(Note: the bannister cannot ambush you if you’re looking right at it.)
4. Inadvertently smash your left hand into the pokey and ornate ornamental bannister at the head of the stairs.
(make sure a hard corner is jammed very precisely between two of your knuckles so that the nerves of your arm are jangled all the way up to your elbow.)
5. Watch it swell.
6. Notice the sudden discoloration.