If an airplane’s passengers start yawning and chewing gum, they might not be over-tired chewing-gum executives–they might be trying to keep their ears from popping. When an airplane changes altitude, air pressure changes often make peoples’ ears go pop, and yawning or chewing can help. If you saw this same thing on a train however, you might wonder what was up. Trains aren’t supposed to change altitude rapidly, are they? Why would your ears go pop on a train?