The eyes often don’t have it. Tennis referees, for example, sometimes mess up when calling a ball in or out. And a new study finds that refs are much more likely to make a mistake by calling a good ball out than by calling a bad ball in.

It takes at least a tenth of a second for us to become aware of an image striking the retina. So we all have to construct our perception of moving objects. And the way the brain works, we consistently think something has gone slightly further than it really has. It’s not surprising then that we misjudge the position of hundred-mile-an-hour tennis balls.