In his mythological poem "Metamorphoses", Ovid tells how the herb comes from the slavering mouth of Cerberus, the three-headed dog that guarded the gates of Hades. As the veterinary historian John Blaisdell has noted, symptoms of aconite poisoning in humans bear some passing similarity to those of rabies: frothy saliva, impaired vision, vertigo, and finally a coma. Thus, some ancient Greeks possibly would have believed that this poison, mythically born of Cerberus's lips, was literally the same as that to be found inside the mouth of a rabid dog.