That is the new and excellent book by Dan Jurafsky, due out this September, and I found it interesting throughout. Here is just one bit:
In fact, the more Yelp reviewers mention dessert, the more they like the restaurant. Reviewers who don’t mention a dessert give the restaurants an average review score of 3.6 (out of 5). But reviewers who mention a dessert in their review give a higher average review score, 3.9 out of 5. And when people do talk about dessert, the more times they mention dessert in the review, the higher the rating they give to the restaurant.
This positivity of reviews, filled with metaphors of sex and dessert, turns out to be astonishingly strong.