帮我看看这个英语笑话讲的是什么?

帮我看看这个英语笑话讲的是什么?
帮我翻译一下这个笑话好吗?
A married couple went to the hospital to have their baby delivered.Upon
their arrival,the doctor said that the hospital was testing an amazing
new high-tech machine that would transfer a portion of the mother's
labor pain to the baby's father.The machine was remarkable as it
required no attachments to the dad but would transfer the pain.
He asked if they were willing to try it out.Both said they were very
much in favor of it.The doctor set the pain transfer to 10 per cent for
starters,explaining that even 10 percent was probably more pain than
the father had ever experienced before.
But as the labor progressed,the husband felt fine and asked the doctor
to go ahead and kick it up a notch.The doctor then adjusted the machine
to 20 per cent pain transfer.
he husband was still feeling fine.The doctor then checked the husband's blood
pressure and was amazed at how well he was doing.
At this point they decided to try for 50 per cent.The husband continued
to feel quite well.
Since the pain transfer was obviously helping the wife considerably,the
husband encouraged the doctor to transfer ALL the pain to him.
The wife delivered a healthy baby with virtually no pain,and the
husband had experienced none.She and her husband were
ecstatic.
When they got home,the postman was dead on the porch

就是说一种机器可以将妻子生产时的疼痛转移到老公身上,生产过程中老公什么都没有感觉到.等到他们回到家时发现邮递员死去了.
也就说孩子不是老公的,是那个邮递员的；