If the animal is small enough to be hand-held, I’ll often go that route since one’s hand can provide a decent setting as well as useful size reference (i.e. “Handamals”). Besides hands, also consider other natural settings of known size (e.g. walnut shell). But here again, the next most important element after choosing your subject is your background: Simple and uncluttered would always be my preference.
source: http://www.thephotoargus.com/inspiration/animalography-exploring-animal-photography/