The deadliest kind of poison is one that strikes without warning, hidden inside something normal or everday. On 29 September 1982, 12-year-old Mary Kellerman of Elk Grove in Illionois, USA, complained about a sore throat. Her parents gave her a Tylenol pill (a US version of Panadol) to help – the same medicine the whole family had been using for years. A few minutes later, they found their daughter collapsed on the bathroom floor. In the panic that followed, nobody considered the harmless painkiller could have been poisoned. But poor Mary Kellerman was dead, before she even reached the hospital.