So I got a Coke Zero out of the fridge, popped the top, and set it down beside the desk. A few seconds later I looked over, and was surprised to see liquid bubbling out of the top.
(Flashing on memories of the old movie The Blob: "It's alive! And it's coming to eat me!")
What happened, as best as my 40-years-since-my-last-science-class mind understands it, is that the soda got cold enough in the fridge that it would have frozen if it had been in a glass. (The old fridge in the utility room, where we keep sodas and other things that won't fit well in the kitchen fridge, tends to run cold.) The pressure inside the can, however, kept actual ice from forming. Once the lid was popped, slush started to form. Because ice expands, the contents overflowed out the top.
I didn't get a shot of the can while it was overflowing. I figured it was more important to slurp off the excess and wipe up what had already dribbled onto the counter. But you can see, in the photo above, the slush that formed inside the can.