Pennyroyal is most commonly used today as a flea repellant and frequently appears as one of the ingredients in natural flea collars for dogs and cats. It can also be used as an essential oil with a drop of oil on a cotton ball placed strategically around the house. Safe from interference by your pet, though. The essential oil is extremely strong and you do not want it to touch your skin. Pennyroyal is a member of the mint family but a rather strong, woodsy mint. It is a low growing creeping perennial plant that does well in shade or sun. As a side note, I live in West Kentucky and a parkway here is named Pennyrile Parkway–a distorted version of pennyroyal. It was so named because wild pennyroyal proliferated in this area. I can picture squirrels and deer and other animals rolling on the plants to get the flea protective properties. Pennyroyal can cause abortion so use with caution.