What Is An Animal?

Biologists have one seemingly objective definition of an "animal" for a particular taxonomic purpose. But, for other purposes, a different definition (which I have come up with, whether or not someone else unknown to me has done the same thing) is appropriate:

An animal is any physical system too complex to be understood as a machine.

Note that this definition has a subjective component, so the classification of a thing is observer dependent. Your automobile, for example, may be a machine from the perspective of your automobile mechanic, but may be an animal, from your perspective. 

The computers I used when they were first available and you assembled them from kits and did a lot of the programming yourself, were machines. But, the computer upon which I am typing this blog post, and the Internet, through which this blog post reaches you, are animals from my perspective and from the perspective of most observers.

When something is a machine, one approach to interacting with it makes sense. When something is an animal, a different approach to interacting with it makes sense.

The way you interact with an animal in this sense is pretty much the same whether the animal would also be classified by a biologist as an animal or not.