Catmint -- or catnip -- is well-known for its intoxicating effect on cats. The odor responsible for the cats' strange behavior is nepetalactone, a volatile iridoid. Researchers have now found that the ability to produce iridoids had already been lost in ancestors of catmint. Hence, nepetalactone biosynthesis is the result of 'repeated evolution.' However, nepetalactone differs considerably from other iridoids with regards to its chemical structure and prop..