During a bizarre bug the other day (http://www.youtube.com/watch?v=vFrBiB80dP4), I noticed that the elevator has a helical thing on the bottom, which appears to mesh with the notches on the rails. It's moved by a worm gear!
It's hard to see on going up because the results window gets in the way, but the spinning helical thingie is visible when it passes over the top for a moment.

It seems pretty spry for a worm! It must get quite hot.