system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5: Why does Vincent Price shake up the champagne in House on Haunted Hill so it won't explode? Doesn't shaking champagne MAKE it explode?
gpt
Champagne bottles are pressurized from a secondary reaction that occurs after bottling. Yeast in the champagne continues to produce CO2, which is trapped in the liquid at far higher pressures than it would be if it had room to expand.

Normally when you open a champagne bottle, all that CO2 gets to start making its way out, which is what causes all the bubbling. However, in order to actually form a bubble, you need enough CO2 to gather together to push against the liquid together. This happens at nucleation sites in the bottle, which are basically any little imperfections in the bottle that trap bits of CO2 together.

When you shake the bottle, you force a bunch of CO2 to be caught at the nucleation sites all at once, which causes a lot of bubbles in the champagne. Eventually, all those bubbles float to the small pocket of air in the bottle and pop. When this happens, you upset a delicate balance of how much CO2 is dissolved in the champagne versus how much is in the pressurized gas. The system will tend to over-correct for a short while, resulting in a bit more of the gas dissolving back into the champagne, lowering the pressure of the air pocket.

Of course, under any circumstances, once you remove the cage from a bottle of champagne, so long as it isn't flat, it will eventually remove its own cork. The pressure is just that high in a champagne bottle.