A zoetrope with about 20 or so little planters arranged around the interior perimeter. When the plants grow, they'll all tilt towards the sun. When you spin it and look at them through the slots it'll look like they're dancing back and forth.

You could also stagger your planting so the serial motion of the progressively larger plants would look like one plant growing very fast.
-- doctorremulac3, Dec 23 2013

random, halfbakery