Have you ever wondered how a tiny bacterium enters your body from the surroundings and causes havoc? A simple explanation could be that it enters your body when you take in the contaminated air or water or through contact. But, how exactly does it move around once inside the body, or even in air or water? It does so in two ways; it either wiggles around with the help of flagellum—a lash-like appendage that protrudes from the body, or uses its body weight (specifically, its head) to propel itself. So what path does it trace when it moves?