system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: When you open your mouth really wide to yawn and it feels like your eardrum pops, what is actually happening?
gpt
Your sinuses and ears are connected via a thin tube called the eustachion tube. Sometimes the tube gets kinked like a hose and the free flow of air is blocked. A change in pressure outside your head, like flying in a plane, can make the air stuck in your head seem pressured. Yawning aligns the tube, allowing the extra pressure air in your head to flow out via your ears.