A six year old comes crying.....

[postman]

[center]A six year old comes crying to his Mother because his
little sister pulled his hair.

"Don't be angry," the Mother says, "Your little sister doesn't
realize that pulling hair hurts."

A short while later, there's more crying, and the Mother goes to
investigate.

This time the sister is bawling and her brother says...

"Now she knows."
[center]