Freezing temp of carbonated beverages I sometimes put bottles of soda in the freezer for 20-30 minutes to get them near frozen (taste SO much better that way).

If I time it just right I'll pull the bottle out and the liquid will appear completely liquid until I loosen the cap - the liquid will then spontaneously turn into slush.

Can anyone explain why that happens?

(this being my first post on the cooking stack exchange I apologize in advance if it's deemed unsuitable)
Obligatory mythbusters: Instant Frozen Beer

It's an instance of Supercooling. The liquid is chilled to below its nominal freezing point, but it doesn't transition to solid, largely because there isn't any growth catalyst for ice crystals. But agitate it, or open it, and the disruption jumpstarts crystal formation, and it freezes solid in seconds.