Got Milk?

Mom keeps pumping in the room to feed me.  She didn't have a chance to do that for a couple of days after I was removed from her womb, therefore her production has been a bit delayed and low.  I heard the nurse tell her, "Good Job.  Just Keep it up."  Mum replied, "I've had these things for a long time.  I might as well get some use out of them."  Everyone in the room laughed.  I just didn't get it.