Say I have a jar full of water covered by a thin plate. Then I turn the jar upside down, holding the plate firmly against the lip of the jar to prevent water from spilling. Then I whisk away the plate so that instead of the plate pushing against the water, only the air beneath the jar is pushing upward. Of course, the water will leave the jar. But what will the geometry of the process be? The water can't leave as a cylindrical slug; intuitively, it seems that the process has instability, so that spontaneous fingering in the air-water interface will break the initial cylindrical symmetry. Maybe Doc Edgerton made high-speed pictures of this? Jim Propp PS: The author of this post disclaims responsibility for all property damage caused by experiments prompted by this question, along with any matrimonial rifts resulting therefrom.