““Any discussion of the sexuality of the digestive tract must inevitably touch on the anus. Anal tissue is among the most densely innervated on the human body. It has to be. It requires a lot of information to do its job. The anus has to be able to tell what’s knocking at its door: Is it solid, liquid, or gas? And then selectively release either all of it or one part of it. The consequences of a misread are dire. As Mike Jones put it, “You don’t want to choose poorly.” People who understand anatomy are often cowed by the feats of the lowly anus. “Think of it,” said Robert Rosenbluth, a physician whose acquaintance I made at the start of this book. “No engineer could design something as multifunctional and fine-tuned as an anus. To call someone an asshole is really bragging him up.””
