Limonene is a terpene known for its intense, fresh citrus scent. Terpenes are fragrant compounds that serve special functions in plants. One reason plants produce limonene is to defend themselves against insects and pathogens.Terpenes serve special functions in plants. Caryophyllene is known for its spicy, woody, peppery aroma it gives to cloves and black pepper. This is likely a defensive mechanism to tell animals and insects, “Don’t eat me!” but it happens that humans like the smell.Why are humans sensitive to compounds found in the cannabis plant, such as THC and CBD? It all relates to our endocannabinoid system. Cannabis is an amazing plant because it adapted to produce compounds that mimic chemicals inside our brains.