DucoNihilum

Could someone explain this to me? I was freezing water bottles for a few hours (4 or so), and picked a water bottle up out of the freezer. It was clear; there was NO ice in it whatsoever. As I was walking to my room, I noticed the entire center of it suddenly froze. The ice was not hard, it was slushy. It came almost instantly, but you could notice a top to bottom movement. It was not pressurized, and it is generic spring water. The bottle was never opened. A video is available here. http://dnpen.com/water.avi Could someone please explain what exactly happened here, how it happened, etc?