Creatures have to breathe. Every monster, alien, dragon or companion beast has to feel like a living, breathing organism with a heartbeat and an attitude. Fantastical things need to feel grounded in something familiar—if a creature has muscles or skin that feel real or evocative of some real world animal, audiences can accept them as plausible. They become alive in our minds and every tooth, feather, tentacle, claw and tuft of fur become real.