[vhfpmr (OP)]

Behind my ear is a groove where the arm of my spex rests. The force it exerts must have all on to be even as much as a gram, so you'd think the tissue it's making an impression in would be soft to the touch, but it ain't so. If I press it with my finger it's so hard and permanent it feels as if someone has machined the groove into my skull.

Yesterday I found a similar groove in my knee where it had been resting against the table leg, and again, it felt so hard it's as if the groove has been filed into my kneecap even though it can't have taken much more than an hour or so to develop. I didn't notice how long it took to disappear again.

What tissue's developing these impressions? It's not soft like pitting oedema, the way sustained gentle pressure deforms it but sudden hard pressure doesn't makes it seem like a non-Newtonian liquid.