system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can't I hear as well when I stretch?
gpt
Apparently, it is the same reason that you can't hear as well when yawning. 
>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, stretching, and a few people develop the ability to open it voluntarily.