Michael Grab must have a deep sense of balance.
First, a photo. Stone balance art by Gravity Glue:
But now, watch Grab make a design like this, from scratch, in three and a half minutes.
I have done rock piles where I am "simply" trying to stack rocks as solidly as possible. Grab seems to relish the challenge of piling rocks in such a way that each one touches the rock beneath on a single point or line:
--With thanks to Robert Krulwich of NPR's RadioLab.