Compare a bituminous roof membrane to a single ply roof membrane.

Single-ply membranes are a assorted and promptly increasing group of sheet materials that are functional to the roof in a single layer. As equated to built-up membranes, they need less on-site labor, and they are usually more flexible and therefore less liable to to cracking and ripping. They are attached to the roof surface by any of several means.

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.