Thanks for bringing it to my attention thenewgreen. The classical "subject of science" is a weird appearance precisely because the limits of their knowledge are not inscribed into the "thing-in-itself" (i.e. we cannot objectively study inner states like thoughts and feelings, therefore there must not be inner states like thoughts and feelings). Of course such a split is likely the consequence of a Cartesian metaphysics where the self-certain knower-thinker can perfect an abstract understanding.

Nonetheless it seems much more likely the case that emotions and thoughts exist throughout the animal kingdom even if we cannot study them objectively or prove them in the way that we can prove the existence of certain external manifestations of behaviour. I would just add a precise distinction on the level of the symbolic or cultural. Animals likely experience feelings and thoughts, but only in the human world are these feelings and thoughts marked by/interpreted through symbolic-cultural material.

Either way there is no way to get inside another's head, animal or human. The advantage with humans (and hence the existence of psychoanalysis) is that a human can tell us that they experience feelings and thoughts with their linguistic capacity. We believe them, even if the subject of science tends not to find the methods and practice of psychoanalysis too convincing.

In any case, I quite like de Waal's specific metaphor about "emotions as organs". I experience my emotions like a 'throbbing organ" (heart, lung, etc.). When they are on they are on: desire, love, fear, sadness. The beat of the organ takes over my body. This is why I like Jacques Lacan's notion of "organ without body" to capture the idea of the emotion as an organ which overdetermines the body as a whole (as opposed to the physical organ which is a part within the body).