The colon is wrinkled and corrugated, somewhat like an accordion or a clothes-dryer exhaust tube, which gives it the large surface area needed for water absorption. In order to inspect this surface thoroughly, the physician blows it up like a balloon, using an air compressor, in order to get the creases out. The stomach, intestines, and colon have a so-called "second brain" wrapped around them, which autonomously runs the chemical factory of digestion. It uses complex hormone signals and nerve signals to communicate with the brain and the rest of the body. Normally a colon's job is to digest food and regulate the intestinal flora. The harmful bacteria in rancid food, for example, creates gas.