Owls  are some of the world's greatest hunters. From head to feet, owls' bodies are built to hunt. Scientists are studying all the things that make owls such great hunters. Most owls hunt at night. The birds have excellent hearing, which helps them find their next meal in the dark. Owls have one ear that is larger and set higher than the other. When an owl hears a sound, it listens closely. Is the sound lounder in its right ear or left ear? Does the upper or lower ear detect the sound first? The information helps the owl find the location of its prey without ever seeing it. Owls don't depend just on their hearing to hunt. After a sound draws an owl's attention, it zeroes in with sight. Many birds have eyes on either side of their heads. But an owl's eyes face forward, like a person's. Images from each eye combine to form a 3-D picture, similar to how we see. That helps owls better judge a prey's size, distance, and speed. An owl's eyes are so large that they can gather lots of light. That helps the owl see better when hunting at night. An owl's eyes are also fixed in their sockets . It can't roll them like we can. Instead, an owl keeps prey in its sight by turning its head. Owls can move their beads nearly upside down and turn them 270 degrees around. Their necks have 14 vertebrae . That's twice as many neck bones as a person has. The blood vessels  thread through holes in an owl's vertebrae. The researchers found that these holes are very large so that the extra space provides an air cushion that protects the vessels. Detecting prey is only the first step for owls. Next they must catch their meals. An owl can fly inches over your head and you can't hear anything. The secret to owls' silent flight is their feathers. Fine "hairs" cover the surface of an owl's wing feathers. And the feathers' edges have soft barbs . Together, they make the sound of air rushing over the owl's wings quieter and less clear. According to text, an owl's eyes  _  .
are small but sharp can function like a person's are on either side of its head can tell how fast a prey is moving