How do you know she is a unicorn?" Molly demanded.

"How do you know she is a unicorn?" Molly demanded. "And why were you afraid
to let her touch you? I saw you. You were afraid of her."
"I doubt that I will feel like talking for very long," the cat
replied without rancor. "I would not waste time in foolishness if I were
you. As to your first question, no cat out of its first fur can ever be
deceived by appearances. Unlike human beings, who enjoy them. As for your
second question --" Here he faltered, and suddenly became very interested
in washing; nor would he speak until he had licked himself fluffy and then
licked himself smooth again. Even then he would not look at Molly, but
examined his claws.
"If she had touched me," he said very softly, "I would have been
hers and not my own, not ever again."
-- Peter S. Beagle, "The Last Unicorn"