"There is no such thing as a cat -- it is just a shape that all manner of imps, hobs, and devilkins like to put on, to gain easy entrance into the homes of men."
-- Peter Beagle, The Last Unicorn

You can see that at the beginning, that they are closer to their natural state of imp and devilkin. But as time goes on they get better at perfecting their disguise. At the end, they almost look like natural creatures, don't they? Well, except when the veil slips.