We are a nation of opinion-holders. Perhaps we always have been: in De Tocqueville’s prophetic study of the American character, the 1835 Democracy in America, he noted that in the United States “public opinion is divided into a thousand minute shades of difference upon questions of very little moment.”

Consider online restaurant reviews, those summaries of the wisdom of the crowd that have become a familiar way to discover new places to eat. Take a look at this sample from a positive restaurant review (a rating of 5 out of 5) on Yelp (modified slightly for anonymity):

I LOVE this place!!!!! Fresh, straightforward, very high quality, very traditional little neighborhood sushi place. ... takes such great care in making each dish ... You can tell the chef really takes pride in his work. ... everything I’ve tried so far is DELICIOUS!!!!

And here are bits of one negative review (a rating of 1 out of 5):

The bartender was either new or just absolutely horrible ... we waited 10 min before we even got her attention to order ... and then we had to wait 45—FORTY FIVE!—minutes for our entrees ... Dessert was another 45 min. wait, followed by us having to stalk the waitress to get the check ... he didn’t make eye contact or even break his stride to wait for a response ... the chocolate soufflé was disappointing ... I will not return.

As eaters we use reviews to help decide where to eat (maybe give that second restaurant a miss), whether to buy a new book or see a movie. But as linguists we use these reviews for something altogether different: to help understand human nature. Reviews show humans at their most opinionated and honest, and the metaphors, emotions, and sentiment displayed in reviews are an important cue to human psychology. The way people talk about skunky beer, disappointing service, or amazing meals is a covert clue to universals of human language and the metaphors we use in daily life—like, why sex is a metaphor for some foods, but drugs are a metaphor for others.

Let’s start by talking about sex.