Zen & The Art of Chicken Sexing

In Japanese commercial hatcheries when chicks are born, trained sex spotters divide them into males and females. This is known as chicken sexing. The divided groups are treated differently. The females are fed because they will produce eggs; a few males are fattened for meat while the rest are deemed useless and early on meet a fate later encountered by all animals in a factory system.

Under pressure from the production line, the chicken sexer must almost instantly choose the correct bin for each chick, a difficult task as cockerels and females look almost exactly the same. Differences appear only after four to six weeks of age.

Almost the same, except for vents, which allows a technique known as vent-sexing. Since the 1930s the Zen-Nippon Chick Sexing School has taught chicken sexers how to vent-sex. Notice "Zen" in the name of the school. Though the technique was effective nobody was quite sure how it was done.
This is rather like those with blindsight, in which the blindsighted person sees without knowing that he sees. Parts of the brain are invisible to the conscious parts.

This is how the training worked. Students picked up a chick, examined its rear, its vent area, and tossed it into one bin or another. There are perhaps a thousand vent configurations that a sexer had to learn to unconsciously recognize. He or she had to diagnose the bird with just a glance. No conscious reasoning here. The master teacher gave a yea or nay as to whether the correct bin had been chosen. That's all. No further explanation was given. Some time later, after learning to work at lightning speed, the student became proficient at vent-sexing, but still could not explain how he knew which bin should be chosen.

Everybody knows that a baseball fielder will fumble if he thinks about catching a high fly ball. A tennis player makes no conscious decision when serving a ball. So, too, with the sexers. They can't explain why. They just do it. Call it intuition. Or call it Zen. Either way, they don't know that they know.