In a doctor's waiting room, a nurse was explaining to a group of women how their infants were weighed. "First of all, we weigh the mother on her own. Then we weigh the mother while she holds her baby. Then we subtract the mother's weight from the combined weight of mother and baby, and we then have the baby's weight."
At which point one of the women said: "Sorry, nurse, but that won't work for me."
"Why not?" asked the nurse.
The woman replied, "I'm the baby's aunt."