Watching the seeds of cranesbill coil up while you watch is always a treat.  The trick is finding the fruit in just the right state of maturity, dry enough to start coiling but not yet detached from the central stalk without a bit of encouragement.  On the ground, the combination of coiling tail and fine hairs that keep the sharp tip pointed down can actually drill the seed into the soil, especially with a few cycles of moist (which uncurls the tail) and dry.