"You may eat all clean birds"—Deuteronomy 14:11.
We are commanded to inspect fowl before consuming them, to ascertain whether they possess the signs that characterize non-kosher birds. Though the Torah doesn't specify signs for non-kosher fowl, rather it supplies us with a list of forbidden fowl species, nevertheless, when studying the group of the listed birds, we can isolate certain common signs that they all share.
"Yet these you may eat of every flying creeping thing"—Leviticus 11:21.
We are commanded to inspect grasshoppers before consuming them, to ascertain whether they possess the kosher sign: "jointed [leg like] extensions above their [regular] legs."
"These you shall eat of all that is in the water"—Leviticus 11:9.
We are commanded to inspect fish before consuming them, to ascertain whether they possess the kosher signs [—fins and scales].
"These you shall not eat of those that [only] chew the cud or of those that [only] have the cloven hoof..."—Deuteronomy 14:7.
It is forbidden to eat any mammal that doesn't possess both kosher signs—split hooves and chewing cud.
"And these you shall detest among the birds, they shall not be eaten"—Leviticus 11:13.
It is forbidden to eat any non-kosher bird.
