Deuteronomy 14:21 "You shall not eat of anything that dies of itself"

The Torah lists those birds and animals which are kosher and are permissible to eat.

However, being kosher does not only mean that the animal or bird is one of those listed in the Torah.

A "kosher" animal must be slaughtered and prepared in a specific way, (see Positive Mitzvah 146).

Take the cow, for example: If the cow is slaughtered according to the rules set by the Torah, (e.g. "Shechitah" etc.) and its meat is prepared correctly, then we are allowed to eat it.

However, if the cow (or any other kosher animal) dies a natural death or is killed improperly, we are no longer permitted to eat it. The kosher animal who dies in this manner is called "Nevelah" and it is forbidden to eat such an animal.