aparently cold=explode

I think diet coke is delicious. cold and delicious. we went grocery shopping last week and left a fidge pack in the trunk of the car. We thought it would be better out there than in the kitchen where we have no room for it. We had just finished up our shopping tonight and opened up the trunk to load up our goodies. what? what is this? What looked like peed on snow was in abundance in the back of the car. the delicious diet coke had EXPLODED. i mean really exploded! It has been down to 4 degrees and night, and dammit i never thought once about my precious DC. It looked like I had shoved a firecracker in the can. the top blew clean off! Not off of just one, all of them had suffered mass destruction. Luckily the clean up was a breeze. i picked up the peed on snow and tossed it outside. crises averted. coke wasted.