Hummingbirds drink nectar using tongues that are so long that, when retracted, they coil up inside the birds’ heads, around their skulls and eyes. At its tip, the tongue divides in two and its outer edges curve inward, creating two tubes running side by side. The tubes don’t close up, so the birds can’t suck on them as if they were straws. Instead, scientists believed that the tubes are narrow enough to passively draw liquid into themselves. That process is called capillary action. Who knew?