Even bacteria can be hosts to smaller symbionts living on them. Some kinds of these extremely tiny bacteria live in various parts of our bodies, and are sometimes associated with inflammation and the resulting disease. But being associated with something isn't necessarily the same as causing that thing. In this study, tiny bacteria living on other bacteria in the mouths of mice were found to reduce the inflammation caused by their bacterial hosts, resulting in less gum disease and bone loss in the jaw. Even when the tiny bacteria were no longer present, their former bacterial hosts were still less disruptive to the mouse mouth.