THE CREATION AND WONDERS OF THE FIFTH DAY ON the fifth day He caused the waters to bring forth abundantly all kinds of winged fowls, male and female, unclean and clean. By two signs are they declared to be clean, by the crop, and by the craw peeling off. Rabbi Eliezer said: (Another sign was) also by the projecting toe of the claw. Two kinds of birds have been chosen for the offering of a burnt sacrifice, namely, the turtle-dove and the young pigeon.