The Kingdom Animalia is extremely diverse, including organisms from about 35 phyla and ranging from sponges to humans. (Yes, I know, some humans are barely distinguishable from sponges.) What common characteristics do all these organisms have that unify them and set them apart from other organisms? No single characteristic does it; rather, it's a unique combination of characteristics. All animals, and no other organisms, are multicellular and heterotrophic (unable to produce their own food) and ingest (as opposed to absorb) their food. Other kingdoms contain organisms that have one or two of these characteristics but only animals - and all of them - have all three.