Both positive and negative feedback play important roles in the physiology of

silty loam

hope this

it's diluted or concentrated

in a diluted solution, you can add a lot more solute but in concentrated only a little more can be added

fumikage isn't really a bird, and tsuyu does have teeth. tsuyu has a transformation quirk which still allows her to be partially human. otherwise we'd have a large frog running around. fumikage has teeth because again, he isn't a bird. his head was a quirk mixture if i'm correct.