I don't know? I was really young, and as far as I can recall I just did it one day.
I always thought it was a muscle in my ears, but I remember looking it up, and it's actually farther back like behind your throat or something. I can't do just one ear at a time, it's all or nothing.
Someone linked this wiki page [1] in the thread. This might be it.
> The effectiveness of the "yawning" method can be improved with practice; some people can achieve release or opening by moving their jaw forward or forward and down, rather than straight down as in a classical yawn,[6] and some can do so without moving their jaw at all by activating the tensor tympani muscle, which is heard by the individual as a deep, rumbling sound.
> During swallowing or yawning, several muscles in the pharynx (throat) elevate the soft palate and open the throat. One of these muscles, the tensor veli palatini, also acts to open the Eustachian tube. This is why swallowing or yawning is successful in equalizing middle ear pressure.
