Guilt by Association

In the case of scary creatures people think up often an association with a body plan of an actual creature people find unsettling- like a spider or a snake or a bat- particularly when it comes to robots and spaceships. If you were to draw an Orc say- there are a bunch of animals you could use as a source- bats faces, hyaenas or other wild doglike things, some of the really fierce baboon faces, maybe the stocky musculature of some fighting dogs.