Scanning electron micrograph (SEM) of a feather from a falcon (Falco sp.). The feather has has a central stem called a rachis (not seen), off which branch numerous parallel barbs (blue). The barbs themselves branch into barbules (yellow), which terminate in tiny hooks (barbicels), which attach to the adjacent barbule. These links allow the feather to present a flat blade. This feather has been cleaned during preparation.