From the catmint plant, Nepeta cataria, we get catnip, which drives many of our feline friends mad.
This necklace depicts nepetalactone, the many molecular constituent of catnip essential oil. While the exact mechanism of nepetalactone isn't yet known, it is likely that it is very similar to cat sex hormones, and affects the cat brain similarly. It affects wild cats (like tigers and leopards) as well as domestic cats. In humans, catmint has a sedative affect. As a bonus, nepetalactone can also repel insects.
The pendant is about a inch long. Shapeways will make and send the pendant alone; the chain is not included.