I have now! Thanks for the recommendation. Consciousness, the subjective experience of what it is like to be something, is very difficult to explain except insofar as there are similar shared experiences that one can make analogy to. I certainly agree with Nagel that entities in human bodies are not equipped to understand the subjective experience of someone whose primary means of sensing the world is through echolocation. This does make me wonder how many bat therians there are, though I would imagine the answer is more than zero.