Einstein and bulldozers puzzle.

Another Einstein puzzle I'm working to formulate a solution. What can Einstein have in common with bulldozers? When I and other folks have been asked this question yesterday, my first thought was: well...we can say that Einstein's work went like a bulldozer through the theoretical physics of the past century. Unfortunately the expected solution was more practical. I'm passing to you the puzzle while I'll try to formulate in a future post the solution that was given to us.