So what of this horse, then, that actually held opinions, and was sceptical about things? Unusual behaviour for a horse, wasn't it? An unusual horse perhaps?

No. Although it was certainly a handsome and well-built example of its species, it was none the less a perfectly ordinary horse, such as convergent evolution has produced in many of the places that life is to be found. They have always understood a great deal more than they let on. It is difficult to be sat on all day, every day, by some other creature, without forming an opinion about them.

On the other hand, it is perfectly possible to sit all day, every day, on top of another creature and not have the slightest thought about them whatsoever.

— Dirk Gently's Holistic Detective Agency by Douglas Adams (Dirk Gently, #1) (Page 4)