A reason for every prohibition......
A joke I heard on the BBC's Old Jews Telling Jokes and rather liked:
A gentile falls in love with an orthodox Jewish girl and asks her to marry him. Before the wedding he visits the rabbi to get tuition on Jewish customs and how he must behave at the wedding.
The rabbi explains that during the ceremony the men and women pray separately. Then the man asks 'Will I be able to sit with my wife at the meal afterwards?' The rabbi say that no, the men and the women eat separately.
'So will I be able to dance with my wife at the celebration?' No, says the rabbi, men and women are forbidden to dance with each other: the men dance with men, and the women dance woth women.
Then the rabbi asks if he has any more intimate questions about marriage.
'Well, sexual positions, rabbi. Is the missionary position allowed?'
'Well we don't call it that, but it's fine.'
'How about with the woman on top?'
'A little bit modern, but it's OK.'
'Kinky, but fine.'
'So what about standing up?'
'Absolutely not: that could lead to dancing!'