PRINCIPLE: Res ipsa loquitur — the thing speaks for itself — applies when negligence may be inferred from the mere occurrence of an accident, without direct proof of the defendant's wrongful act. The doctrine operates when: (1) the accident would not ordinarily occur absent negligence; (2) the instrument or agent causing injury was within the exclusive control of the defendant; and (3) the plaintiff did not contribute to the accident. Once these conditions are established, negligence is presumed unless the defendant provides an explanation inconsistent with negligence.

FACTUAL SCENARIO: A customer entered a supermarket operated by MegaMart Ltd. and was shopping in the cereal aisle when a large wooden shelf unit collapsed without warning, striking her and causing serious injuries to her shoulder and arm. The customer had not touched the shelf, knocked it, or done anything to destabilize it. There were no warning signs posted. Security cameras showed no other customers or store employees near the shelf immediately before the collapse. The shelf had been installed by MegaMart's maintenance team six months prior. MegaMart's records showed no documented inspections, maintenance schedules, or safety audits of shelf units had been conducted since installation. Expert testimony at trial established that properly maintained and regularly inspected shelves do not spontaneously collapse during normal store operations. The customer filed suit against MegaMart for negligence. MegaMart argued it had no actual knowledge that the shelf was defective and presented no alternative explanation for the collapse other than "unknown causes." The plaintiff presented no direct evidence of MegaMart's specific negligent act — such as overloading, improper installation, or deliberate failure to inspect — only circumstantial evidence that the collapse occurred.