Difference Between a Baby Hen & a Baby Rooster | eHow
"Vent sexing requires applying a squeezing hold to the chick to clear its digestive tract and expose its anal opening. Once this is cleared, the chicken sexer can visualize a tiny raised lump inside the anus of male chicks. In contrast, female chicks have no lump."
It sounds unpleasant- squeezing out the excrement
