Elderly foreign tourists are tapping Mexican pet shops for a drug used by veterinarians to put cats and dogs to sleep that has become the sedative of choice for euthanasia campaigners. Tourists from as far as Australia have travelled to Mexico to buy liquid pentobarbital, which causes a painless death in humans in less than an hour, right-to-die advocates say. Clutching photos of the bottled drug to overcome a lack of Spanish, they have maps sketched by euthanasia activists to locate back-street pet shops and veterinary supply stores near the US border. There they can buy a bottle for $35...