We organize according to resemblances. Our need to compare is psychological and emotional. Poets try not only to relate to what is familiar, but they try to discover resemblances that no one had noticed before.
Poets express discoveries of likenesses through figures of speech like simile and metaphor.
Some people think figures of speech are unnatural but language itself is nothing but a figure of speech We use a word when we mean a thing. No question of a real bull. Metaphor, since unqualified, is usually stronger than simile. More concentrated, hits with greater impact. The head of a seal may seem too much like a poodle.