  The fluid dynamics video shows rigid, spatially asymmetric bodies interacting
with oscillating background flows. A free rigid object, here a hollow
"pyramid," can hover quite stably against gravity in the oscillating airflow
with a zero mean, when its peak speed is sufficiently high. We further show in
shadowgraph imaging how this asymmetric body sheds vortices in such an unsteady
flow, thus enabling the body to "ratchet" itself through the background flow.
