By Ross Pitcairn for Spring 2013 Get Wet.
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Air comes out of solution as water cools to freezing. If frozen quickly, both large and small bubbles are formed. Pure water freezes first at the periphery, trapping bubbles in the interior.
When a water balloon is popped by a pellet gun, the contracting rubber skin and pressure drop disturbs the surface. The water seems to float momentarily before falling. Filmed at up to 1000 fps by a Casio EX-ZR100.