Beads.

Saw this man who sat, deep in thought, as his hand worked it's way repeatedly around a string of beads. 

I became almost hypnotised by the way the join on the beads edged anti-clockwise round and round, And it didn't occur to me to sketch him until it was almost too late. Just managed to get his face, and the hand with the beads. 

And it turns out that is all that was needed.