Machine to share pain

A married couple went to he hospital to have their baby delivered. Upon their arrival, the doctor said he had invented a new machine that would transfer a portion of the mother's labour pain to the father.

He asked if they were willing to try it out. They were both very much in favour of it. The doctor set the pain transfer dial to 10% for starters, explaining that even 10% was probably more pain than the father had ever experienced before.
But as the labour progressed, the husband felt fine and asked the doctor to go ahead and bump it up a notch. The doctor then adjusted the machine to 20% pain transfer. The husband was still feeling fine.

The doctor checked the husband's blood pressure and was amazed at how well he was doing. At this point they decided to try for 50%.

The husband continued to feel quite well. Since it was obviously helping out his wife considerably, the husband encouraged the doctor to transfer ALL the pain to him.

The wife delivered a healthy baby with virtually no pain.
She and her husband were ecstatic.
When they got home, the mailman was lying dead on their porch