All adult human beings are actors. We grow up learning how to suppress the way we really feel. Over time the layers of our pretence build up, and some of us become so adept at concealment that we really have forgotten who we are. Our personalities appear entirely different from our true nature, and by the time this out of balance approach to life leads to the offices of a Bach practitioner there are multiple layers of hardened emotion to be got through before the real person underneath can even begin to emerge.
Animals are in general less complex.
The layers of deceit have not built up. Some may still hide their emotions, perhaps in the Agrimony way, by playing the clown when there is torture inside, or perhaps in the Water Violet way of withdrawing from companions to deal with things alone. They are less likely to be harbouring twenty other mental states hidden under this first layer. If this general rule is true then selecting remedies for animals really is a simple process of empathy and understanding, as Nora Weeks used to point out. Where it becomes harder is at those points where communication between species breaks down - in other words, when we misread or simply fail to read what an animal is telling us.