Here's a fun party trick. Hand your guests six long steel nails. Then show them a wooden dowel, about the same in length and diameter as the nails, which is standing securely on a base. (Obviously you'll have to prepare that ahead of time.)
Now ask your guests if they can balance all six nails on top of the dowel at the same time — without touching the base or the surface that the base sits on. I won't explain the simple solution in case you want to figure it out yourself (the explainer part of the video starts at 19:00).
Thanks Mr. Puzzle!