Res Ipsa Loquitur is a legal doctrine used in tort law that means "the thing speaks for itself." It applies when an accident occurs, and the cause is obvious, even without direct evidence. This principle allows a plaintiff to prove negligence by showing that the event typically does not happen without someone's negligence. For example, if a patient undergoes surgery and a surgical instrument is left inside their body, Res Ipsa Loquitur can be invoked. In such cases, the burden of proof may shift to the defendant to show they were not negligent, as the incident itself suggests a failure in care.