The gut is home to trillions of bacteria that are constantly sensing their surroundings in order to survive and thrive. New research shows that beneficial gut microbes, especially the common bacteria Clostridia, detect a wide range of chemical signals produced during digestion. These signals include byproducts of fats, proteins, sugars, and even DNA. Microbes use specialized sensors to move toward valuable nutrients. Lactate and formate are particularly important fuel sources for these bacteria. This ability to perceive the environment is crucial for human health.