Res ipsa loquitur shifts burden to defendant when the accident itself indicates negligence, creating a rebuttable presumption in civil law. The principle of res ipsa loquitur is an evidential rule in negligence cases allowing an inference of defendant's negligence when the harmful instrumentality was under the defendant's control and the event does not ordinarily occur absent negligence, thereby shifting the evidential burden to the defendant to rebut with a non-negligent explanation; its operation is confined mainly to civil tort proceedings and has limited application in criminal negligence trials.