To answer your question, let's think about what makes soda bubbly. Soda and other fizzy drinks actually have dissolved carbon dioxide in them. As you may know, carbon dioxide is a gas at room temperature. Plants breathe carbon dioxide in for photosynthesis, and humans breathe carbon dioxide out. But how do we get a gas like carbon dioxide get into a liquid like water? One good way is pressure. You can grab some carbon dioxide and, with a little bit of pressure, force it into a liquid.

If you don't hold your drink under pressure, like when you leave a soda on the counter overnight, the carbon dioxide escapes and your drink will go "flat". A can of soda is made under pressure. It's not a lot of pressure though, which is why you only hear a small hiss as soon as you pop the tab. There is a small layer of undissolved carbon dioxide at the top that escapes to make that sound.

Now when you shake the can, you move the soda all around inside and you move the carbon dioxide around, too. Some of the carbon dioxide bump into the walls and stick there. These bubbles are under a lot of pressure; they want to grow bigger, but they can't. As soon as you open the can, the pressure is lowered so the volume of the bubble increases – violently – as the bubbles try to escape. This is what causes the explosion when you open the can. The growing and escaping bubbles push the soda out of the way and make a huge mess.

To demonstrate this, you can try an experiment (if you have permission – it might get messy). Shake a can of soda, and then flick the sides of the can. Start from the bottom and work your way to the top. Now open the can. If you did it right, the flicking should have knocked the bubbles that stuck to the side back to the top of the can, and your soda won't explode!

Another interesting point about dissolving gases in liquids is that the amount of gas that will stay in depends on the temperature. If you've ever left a plastic soda bottle in the car on a hot day, you'll notice that it feels like it's under a lot of pressure. And if you open the bottle, you might get a frothy mess of soda all over yourself. This indicates that liquids can hold less gas when they're hot and more gas when they're cold.