milking chickens

Ok, so my aunt teaches her kids some sign language before they can talk so that they can communicate without screaming. So one of my cousins was doing the sign for milk and I could not figure out why that was the sign until my aunt said "It is like you are milking a cow." Well that made total sense. Then my other cousin said, "Yea like a cow or a chicken, like milking a chicken!" It was really funny...