Rashi expressed the opinion that the reference to mother's milk must exclude fowl from the regulation, since only mammals produce milk.[32] According to Shabbethai Bass, Rashi was expressing the opinion that the reference to a mother was only present to ensure that birds were clearly excluded from the prohibition;[33] Bass argued that Rashi regarded the ban on boiling meat in its mother's milk to really be a more general ban on boiling meat in milk, regardless of the relationship between the source of the meat and that of the milk.[33]