There’s a classic short story about a young woman who is recovering in a hospital. She wakes up, looks up from her bed, and somehow, every person she encounters has the head of an animal. The young nurse is a cat, the doctor is wolf, her fiance—gasp—is a snake. She looks in the mirror—she has the head of a fawn.
The reader is not too baffled, right? The point of the story is pretty darn clear. But take a look at your characters. What animal’s characteristics do they display—on the outside, and on the inside? Could you delve into that a little more? You’d never say “She was like a cat” of course. You can do better than that! But might you say, “I could almost hear her purring”?
You’d never write “He was like a snake.” But he might hiss, or slither, or entwine himself around … something.
See what animal instincts your characters have. Do they know it? Do the others in their world? How can you use that?