A surgeon operates on the wrong leg — the consent form said 'left', the leg marked 'right'. Wrong-site surgery is negligence per se — duty (surgeon-patient), breach (operating despite the mismatch), damage (harm) — the Bolam test (accepted practice: WHO checklist — sign-in, time-out, sign-out) defines the standard breached. Consent for the correct procedure doesn't cover the wrong site. Criminal prosecution (304A) needs gross negligence; civil claims need compensation proof. The checklist exists because memory fails — systems beat good intentions.