We've all heard (and probably experienced) the long-running joke that stepping on a Lego is the absolute worst.
People have determined this is due to the bricks' high compressive strength, small size, and sometimes sharp edges.
As far as edges are concerned, consider a standard 2x2 brick:
While the 6 faces are fairly harmless, if the brick were somehow angled such that a person put all their weight on an edge, or (god forbid) one of the 8 corners, it would really hurt.
So the question is: What Lego part, or assembly of Lego parts, would maximize both
(a) small size, and
(b) sharp edges/points pointed upwards when laying on the ground?