henry's pocket...

...more formally known as a cutaneous marginal pouch,  the pocket is  a ' fold of skin forming an open pouch on the lower posterior part of the external ear'.
Nearly all domestic cats have these and it is thought to help cats detect high pitched sounds while hunting.
Not all dogs have Henry's pocket but some do, seemingly those with 'sticky up ears'! (so yes Astro has Henry's pockets!) and they assist in folding or flattening of the ear rather like an accordion pocket.
And bats and weasels have them...who knew!!

Scarily a cat lover has written a poem about Henry's pocket...but definitely NOT going down that road!
Though it would be good to know who Henry was.