[The expression "unclean" is a rendering generally of the Heb. tame, "(ceremonially) polluted," "defiled," "unclean," and the Gr. akathartos, "impure," "defiled," "unclean."] Animals declared by the Law of Moses to be unfit for either food or sacrifice. The purpose in distinguishing certain animals as clean and others as unclean was apparently two-fold—dietary and religious. Whether the distinction between clean and unclean animals was based exclusively on their habits and on the unwholesomeness of their flesh as food is not altogether certain, but the fact remains that from very early times—centuries before the giving of the Mosaic law—the distinction was clearly recognised (see Gen 7:2, 3; 8:20). Generally speaking, at least, animals designated as clean are herbivorous in diet and comparatively gentle in disposition, whereas birds and animals listed as unclean are carnivorous. With quadrupeds and sea animals the distinction between clean and unclean is clear. An animal is clean if it parts the hoof, is cloven-footed, and chews the cud (Lev 11:3, 8, 26). To be clean, a creature of the water must have both fins and scales (vs. 9-12). For the various kinds of fowl no basic rule is stated. There is only an enumeration of the unclean fowl (Lev 11:13-20; cf. Deut 14:12-18). Because it flies, the bat is included among the birds (Lev 11:19; Deut 14:18). Of insects, the locust, bald locust, cricket (RSV), and grasshopper are listed as clean; others are unclean (Lev 11:20-23). All small creeping animals are declared to be unclean (vs. 29, 30, 41, 42). A man who incurred uncleanness by contact with an unclean creature was required to wash his clothes and to remain unclean for the rest of the day (vs. 24-28, 31, 32, 39, 40; ch 17:15). By contact with an unclean creature any earthen vessel, food, water, seed grain, or clothing also became unclean (ch 11:32-38) -- Seventh-day Adventist Dictionary.