Pennyroyal, also referred to as European pennyroyal to distinguish the herb from false pennyroyal, is a member of the mint family native to most of Europe and Asia. Although its common name stems from a corruption of Pulioll-royall, the name given to the plant by medieval herbalists, pennyroyal is also known as Run-by-the-Ground and Lurk-in-the-Ditch, likely in reference to its invasiveness. The nickname Pudding Grass evolved from its old-time use as a stuffing ingredient in a type of sausage known as “hogs pudding.” Due to the toxicity of a compound called pulegone, internal use of pennyroyal is no longer advisable. The dried herb is, however, an excellent deterrent to fleas and other pests.