The feline approaches its prey. Slowly at first, then crescendoing to a pounce that lands near, but not on the unmoving target. The cat bats an investigatory paw, then claws its target and yanks it faceward. But the cat does not bare its fangs; it does not bite. It closes its eyes and rubs the prey—a sock flecked with bits of dried herb—across its whiskers, then falls to the ground, its body humming with purrs that oscillate into soft meows.

Most cats love nip, and many cat owners love watching their companions nip out. But not all cats freak out when they sniff the fragrant herb—some just don't react at all. Which is a shame, because catnip can be a boon for under-stimulated indoor kitties, who can get so stressed with lack of activity that they can develop diseases. However, a new study shows that there might be some alternatives for the nip-immune. At least three other plants emit chemical odors capable of turning your furball into a puddle of purr, and one of them is potentially more potent than nip itself. The finding doesn't just give cat owners more options to sprinkle on their pet's cardboard scratchbox: It might help solve the chemical mystery of why cats love nip so much.

Mr. Chibbs and his dime bag. Sean Alexander/WIRED

The fun starts when cats catch the scent of nepetalactone, catnip's active ingredient. It's a terpene, which is an aromatic compound in the same family as the skunky chemicals that give marijuana its characteristic funk. Scientists figured out the nepetalactone-cat link back in the 1940s, but still don't know which genes make some cats start pawing themselves like teenage ravers whenever they catch a whiff of eau de nip. Which would be interesting, given that catnip doesn't seem to serve any real genetic purpose: It's not a food or a sexual stimulant, it's basically just a recreational narcotic. And figuring out that genetic link wasn't just a matter of sequencing kitty spit from a nippin' Nebelung and comparing it with DNA from some straight edge Siamese. "There are also environmental causes for the catnip response, because in our observations some cats won't respond when they are feeling threatened, or others when they are pregnant," says Tony Buffington, cat veterinarian emeritus at UC Davis.

In some ways, this study adds even more confusion, because it's not just nip that turns cats on. Sebastian Bol, molecular biologist and owner of the Cowboy Cat Ranch in Texas pardner'd up with several southern California cat clinics to test three additional plants—silver vine, Tatarian honeysuckle, and valerian root. With 100 different cats, he rubbed the plant matter on a sock or a square of carpet, and set the material in the cats' line of sight. Then he waited. If the cat approached and backed away, he considered that a denial. "Animals tend to move towards things they like, and back away from things they consider threats," says Buffington. After each success or denial, he'd wait about five minutes for the cat to relax, then try again with another plant type. The response rate was striking: Almost 80 percent of the cats responded to the silver vine (a higher response rate than even nip, which got less than 70 percent of the cats high), and roughly 40 percent each for valerian root and honeysuckle.

Interestingly, some cats who didn't react to nip would react to one of the other stimulants, and only 23 of the cats in the study responded to all four plants. And six cats responded to nothing at all. The rest of the cats responded to one, two, or three of the plants, with varying degrees of overlap. Catnip is the only plant with nepetalactone; the other plants have similar molecules. So there's some variation in the sensitivity of cats' neuronal receptors responsible for triggering that contorted catnip twerk. That's good news for cat owners whose pets don't respond to nip, and are looking for some chemical alleviation for the homebound cat blues.

But the study still leaves a lot of mysteries as to why cats respond at all. It found no correlation with age, sex, or even personality types among the different plant types. "One thing I was surprised by was the fact that the cats with shy or scared personality types responded just as readily as the more affectionate or friendly cats did," says Buffington.

After getting such a positive response from silver vine, Bol contacted some friends at Big Cat Rescue in Tampa, Fl, to partially repeat his experiment on some tigers and bobcats. As expected, the tigers turned their noses at both the silver vine and the nip—they are the teetotalers of the cat family. The bobcats mostly ignored the catnip, but rolled around with the silver vine like joyful kittens.

The study can't conclusively say what causes the response, but it might help some cat owners tame their cabin-fevered felines. "This provides cat owners alternatives to enrich the lives of their confined cats," says Buffington. "Cats that are left alone with little stimulation are at a greater risk for obesity, which can lead to many other health problems." Cats love novelty, and spending part of their day blissed out on plant matter might help them cope with the sensation of living with a hairless, erratic ape.