What is Animal?

Legal Definition
Animals are multicellular, eukaryotic organisms of the kingdom Animalia (also called Metazoa). The animal kingdom emerged as a basal clade within Apoikozoa as a sister of the choanoflagellates. Sponges are the most basal clade of animals. Animals are motile, meaning they can move spontaneously and independently at some point in their lives. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their lives. All animals are heterotrophs: they must ingest other organisms or their products for sustenance.

Most known animal phyla appeared in the fossil record as marine species during the Cambrian explosion, about 542 million years ago. Animals can be divided broadly into vertebrates and invertebrates. Vertebrates have a backbone or spine (vertebral column), and amount to less than five percent of all described animal species. They include fish, amphibians, reptiles, birds and mammals. The remaining animals are the invertebrates, which lack a backbone. These include molluscs (clams, oysters, octopuses, squid, snails); arthropods (millipedes, centipedes, insects, spiders, scorpions, crabs, lobsters, shrimp); annelids (earthworms, leeches), nematodes (filarial worms, hookworms), flatworms (tapeworms, liver flukes), cnidarians (jellyfish, sea anemones, corals), ctenophores (comb jellies), and sponges. The study of animals is called zoology.
-- Wikipedia
Legal Definition
Property. A name given to every animated being endowed with the power of voluntary motion. In law, it signifies all animals except those of the him, in species.

2. Animals are distinguished into such as are domitae, and such as are ferae naturae.

3. It is laid down, that in tame or domestic animals, such as horse, kine, sheep, poultry, and the like, a man may have an absolute property, because they coutiaue perpetually in his possession and occupation, and will not stray from his house and person unless by accident or fraudulent enticement, in either of which cases the owner does not lose his property. 2 Bl. Com. 390; 2 Mod. 319. 1.

4. But in animals ferae naturae, a man can have no absolute property; they belong to him only while they continue in his keeping or actual possession; for if at any they regain their natural liberty, his property instantly ceases, unless they have animum revertendi, which is only to be known by their usual habit of returning. 2 Bl. Com. 396; 3 Binn. 546; Bro. Ab. Propertie, 37; Com. Dig. Biens, F; 7 Co. 17 b; 1 Ch. Pr. 87; Inst. 2, 1, 15. See also 3 Caines' Rep. 175; Coop. Justin. 457, 458; 7 Johns. Rep. 16; Bro. Ab. Detinue, 44.

5. The owner of a mischievous animal, known to him to be so, is responsible, when he permits him to go at large, for the damages he may do. 2 Esp. Cas. 482; 4 Campb. 198; 1 Starkie's Cas. 285; 1 Holt, 617; 2 Str.1264; Lord Raym. 110; B. N. P. 77; 1 B. & A. 620; 2 C. M.& R. 496; 5 C.& P. 1; S. C. 24 E. C. L. R. 187. This principle agrees with the civil law. Domat, Lois Civ. liv. 2, t. 8, s. 2. And any person may justify the killing of such ferocious animals. 9 Johns. 233; 10. Johns. 365; 13 Johns. 312. The owner, of such an animal may be indicted for a common nuisance. 1 Russ. Ch. Cr. Law, 643; Burn's Just., Nuisance, 1.

6. In Louisiana, the owner of an animal is answerable for the damage he may cause; but if the animal be lost, or has strayed more than a day, he may discharge himself from this responsibility, by abandoning him to the person who has sustained the injury; except where the master turns loose a dangerous or noxious animal; for then he must pay all the harm done, without being allowed to make the abndonment. Civ. Code, art. 2301. See Bouv. Inst. Index, h. t.
-- Bouviers Law Dictionary
Legal Definition
Any animate being which is endowed with the power of voluntary motion. In the language of the law the term includes all living creatures not human. Domitoe are those which have been tamed by man; domestic. Eeroe natures are those which still retain their wild nature. Mansuetoe natures are those gentle or tame by nature, such as sheep and cows. See Animals of a base nature.
-- Black's Law Dictionary
Legal Definition
Any animate thing not human endowed with power of voluntary motion.—Bouvier Law Dictionary.
-- Ballentine's Law Dictionary