A sage, Yochanan the son of Dahavi, revealed a secret told to him by the “ministering angels” — what causes children to be born disabled. Children are born lame because their parents had anal sex! Children are born mute because their father kissed their mothers’ private places! Children are born deaf because their parents spoke while engaged in sexual relations! Children are born blind because their fathers looked at their mothers’ private places! The scholars asked: From the words of the ministering angels we can imply that one is forbidden to speak during sexual relations, but Rabbi Elazar customarily spoke with his wife while engaged in sexual relations. Moreover, their children were exceptionally lovely. Answer: One is forbidden to speak of matters which are not related to desire and foreplay, but verbal foreplay with one’s wife is permitted. One of the scholars, R’ Yochanan, said that the reasons stated above for children’s disabilities are not accepted by the other sages. In their opinion one may do whatever one wishes during conjugal relations; as they put it, “Whatever a man wants to do with his wife he does. It is like meat from the butcher; if he wishes to eat it salted he does so, if he wishes to roast it he does so, baked he does so, boiled he does so.” One of the scholars, Amimar, said that you must conclude the “ministering angels” mentioned above are not truly angels, but flesh and blood scholars. Had they truly been angels we would have had to rule Halacha in accord with them, for they are expert in the reasons why children are born disabled. The sages also determined nine reasons why children are born with negative characteristics. One is when a woman asks her husband to have sexual relations with her; her children are the sons of impudence. The scholars asked: Did not another sage rule just the opposite, that a woman who asks her husband for sexual relations will produce sons unequalled even in the days of our teacher Moses? Answer: If she verbally demands, they will have impudent children, but if she hints, she will have worthy sons.
(Babylonian Talmud, Tractate Nedarim 20a-b)