In the eagle, the retina's fovea has one million cells per mm2 as compared to 200,000 per mm2 in humans. Eagles have a second fovea and three eyelids (two of which are visible).[2] The second fovea in eagles gives them better and sharper vision while the long, narrow ribbon-shaped area that connects the two eagle foveas is inferred to be a third fovea. The phenomenon of an eagle turning its flexible head almost 270 degrees,[3] while sitting or flying, is attributed to the fact that when its large head is turned fully its eyes are also turned, unlike a human.