Altitude, pressure and toothpaste

I flew back from Sydney (which is at sea level) to Armidale (which is 1000m / 3300ft above sea level) last night. I know perfectly well that this means that there is a non-trivial pressure difference between the two altitudes.

Once again, though, without thinking anything of it, I uncapped the tube of toothpaste and, squiiiiiirt, the toothpaste tube gushes more toothpaste than any toothbrush can usefully use until the pressure is equalised.

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