Owls don't need eyes in the back of their heads to see what's behind them — they can just swivel their heads all the way around. In fact, many owl species, such as the barred owl, can rotate their heads 270 degrees in each direction, which means they can look to the left by rotating all the way to the right, or vice versa. But how do they do it without severing their arteries or preventing blood from reaching the brain?