Books can be attributed to "Unknown" when the author or editor (as applicable) is not known and cannot be discovered. If at all possible, list at least one actual author or editor for a book instead of using "Unknown".
Books whose authorship is purposefully withheld should be attributed instead to Anonymous.
Thompson's essay on "Life and Mind" is worth 10 stars. In it, he clearly articulates a number of fascinating connections between cognition and the process of living (ala Maturana and Varela). I got more out of this essay than Thompson's 500 page book on the same topic. I didn't find the rest of Emergence and Embodiment particularly engaging or edifying.