An owl can turn its head up to 270 degrees, three-quarters of a circle. In people, a hard neck twist can tear blood-vessel linings, causing clots that can cut off blood to the brain.
One major artery to an owl's brain passes through neck-bone holes about ten times its width, so it can shift during a twist.
Owl neck vessels also cross-connect, so if one route is blocked, blood reaches the brain another way.