Rav Chisda asked how Noah knew (before the giving of or ) which animals were clean and which were unclean. Rav Chisda explained that Noah led them past the Ark, and those that the Ark accepted (in multiples of seven) were certainly clean, and those that the Ark rejected were certainly unclean. Rabbi Abbahu cited , "And they that went in, went in male and female," to show that they went in of their own accord (in their respective pairs, seven of the clean and two of the unclean).