To explain the idea of milk being made as needed, I relate it to every
person's saliva for the mother.  Just as a mother never runs out of saliva, a
body fluid, her body will produce milk for baby when stimulated.  I explain
that when we eat sour foods, we have more saliva, on demand.  And, when baby
nurses the sucking and hormones cause the body to make milk, as the baby
nurses.
Barb