Zoopharmacognosy is a behaviour in which non-human animals self-medicate by selecting and ingesting or topically applying plants, soils, insects, and psychoactive drugs to prevent or reduce the harmful effects of pathogens, toxins, and even other animals. The term derives from Greek roots zoo ("animal"), pharmacon ("drug, medicine"), and gnosy ("knowing"). An example of zoopharmacognosy occurs when dogs eat grass to induce vomiting. However, the behaviour is more diverse than this. Animals ingest or apply non-foods such as clay, charcoal and even toxic plants and invertebrates, apparently to prevent parasitic infestation or poisoning. Whether animals truly self-medicate remains a somewhat controversial subject because early evidence is mostly circumstantial or anecdotal; however, more recent examinations have adopted an experimental, hypothesis-driven approach. The methods by which animals self-medicate vary, but can be classified according to function as prophylactic (preventative, before infection or poisoning) or therapeutic (after infection, to combat the pathogen or poisoning). The behaviour is believed to have widespread adaptive significance. History and etymology In 1978, Janzen suggested that vertebrate herbivores might benefit medicinally from the secondary metabolites in their plant food. In 1993, the term "zoopharmacognosy" was coined, derived from the Greek roots zoo ("animal"), pharma ("drug"), and gnosy ("knowing"). The term gained popularity from academic works and in a book by Cindy Engel entitled Wild Health: How Animals Keep Themselves Well and What We Can Learn from Them. Mechanisms The anti-parasitic effect of zoopharmacognosy could occur by at least two mechanisms, namely demonstrated through the modes of deglutition or ingestion. First, ingested material may have pharmacological antiparasitic properties, such as phytochemicals decreasing the ability of worms to attach to the mucosal lining of the intestines or chemotaxis attracting worms into the folds of leaves. Additionally, many plants have trichomes, often presented as hooked and spiky hairs, that can attach to parasites and dislodge them from the intestines. Another possible mode of action is that the ingested material may initiate a purging response of the gastrointestinal tract by rapidly inducing diarrhoea. This substantially decreases gut transit time, causing worm expulsion and interruption in the life cycle of parasites. This, or a similar, mechanism could explain undigested materials in the faeces of various animals such as birds, carnivores and primates. The topical application of materials is often used by animals to treat wounds or repel insects. When plant leaves are chewed and then directly rubbed onto fur, compounds from said leaves are