The executive toy that clicked away on office desks through the 80s, rebuilt from photos of a classic chrome cradle on a black base (turn your sound on). Pull a ball out and let it go: it strikes the row, and the ball at the far end flies out as if the blow had passed straight through. Pull out the second or third ball and the ones beyond it come too - and the same number leave the other side. Tap a ball to lift it and let it fall, or grab a swinging one to stop it. On a computer, Space drops one ball, 2, 3 and 4 drop that many, and Escape stops them all. The click is a pressure wave crossing the steel in a fraction of a millisecond.