Transferring the Pain

A Husband and Wife go to the hospital to deliver their child.
The doctor meets them and tells them that he has a new system that will allow the father to take part or all of the mothers labor pains.
They both agree and the delivery begins.
The doctor turns the dial to 10%, so that the father will take 10% of the mothers pain.
The husband says he feels fine, so the doctor puts it up a notch.
The husband still feels fine, so the doctor puts it up to 30%.
The husband still feels fine, so it goes up to 50%.
The husband tells the doctor to go ahead and put it up to 100%.
The husband still feels fine and the child is delivered and the wife felt virtually no pain at all.
They both go back home with their child, where they find the mailman dead on their steps!!!