Wording of this Handout:
Know how a zip works? Two lines of stubs, which lock into each other when a little machine pulls them closer.
Long before anyone invented the zipper, birds were flying around with millions of them.
Feathers are marvels of engineering.
They are light, and strong, and specially designed to catch the air.
But look closer and you will see that each feather is covered by tiny ribs, or barbs. Every barb has even smaller things along the sides called barbules, and along the edges of each barbule are sometimes millions of microscopic hooks called barbicels.
All these tiny hooks or barbicels fit into the hooks along the adjacent barbule, forming a uniform mat. Its just like weaving.
And what happens when the feather is ruffled, and the hooks come undone?
The bird runs its beak along the feather and zips it all together again.