system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does yawning temporarily block or alter your hearing?
gpt
First we have to mention the Eustachian tube.

The Eustachian tube is like a pressure regulator that prevents your ears from popping out. One end of this tube is found between the eardrum and the cochlea (where the hearing is actually done using fine hairs), and the other end behind the nasal cavity. Whenever, the pressure changes in your ears, this tube opens and balances the pressure. This tube is normally closed all the time and opens when you chew something, yawn, stretch or when there is a necessity to balance the pressure (when you travel in an airplane).

The reason why we don’t hear any external sound while yawning is that, when the Eustachian tube is opened, the source of the sound is now actually two – The ear canal and the Eustachian tube. The sound through the Eustachian tube fills the middle ear, which thereby also reduces the ability to amplify the sound from the ear canal. This is the reason, why we hear our internal sounds more, when we yawn or stretch. This opening of the tube is just temporary while yawning.