So, I’ve always known that airplane cabins are pressurized to an altitude well above sea level. As a practical matter, one usually goes merrily (or not) along without noticing any physical effects. However, as any novice physicist will tell you, the change in pressure–even inside a pressurized cabin–can have real-world manifestations.
This happened to us mid-flight to New York.
Libby opened Emerson’s (now highly pressurized) sippy cup. This produced a Bellagio worthy fountain of water… which sprayed Emerson and the passengers in the row behind us! With air tightness like that it’s no wonder that sippy cups hold water so well.
It was rather embarrassing but (on reflection) also wildly funny. And, thankfully the other passengers were gracious.