The punchline is too long.
Because he is dead. ((I came up with this joke when I was very tired.))
If you have to explain it then it is not that good.
What do you call a nun that sleep-walks a) A Roamin' Catholic b) An unconscious habit
Don't worry, he will inform you after delivery of the punchline has taken place. Just a joke!
They both take out everyone with just one punch.