A brush hog is a heavily built rotary mower. Typically these mowers attach to the back of a farm tractor using the Three-point_hitch an is driven via the Power Take Off (PTO). It has blades that are not rigidly attached to the drive like a lawnmower blade, but are on hinges so if the blade hits a rock or stump, it bounces backward and inward, and then centrifugal force makes it go outwards again.