"Domestic and many wild cats (including cougars, bobcats, lions, and lynx) respond to the nepetalactone in catnip. However, not all cats react to catnip. The behavior is inherited as an autosomal dominant gene; 10-30% of domestic cats in a population may be unresponsive to nepetalactone. Kittens will not show the behavior until they are at least 6-8 weeks old. In fact, catnip produces an avoidance response in young kittens. The catnip response usually develops by the time a kitten is 3 months old.
When cats smell catnip they exhibit a range of behaviors that may include sniffing, licking and chewing the plant, head shaking, chin and cheek rubbing, head rolling, and body rubbing. This psychosexual reaction lasts for 5-15 minutes and cannot be evoked again for an hour or more after exposure. Cats that react to nepetalactone differ in their individual responses.
The feline receptor for nepetalactone is in the vomeronasal organ, located above the feline palate. The location of the vomeronasal organ may explain why cats do not react from eating gelatin-enclosed capsules of catnip. Nepetalactone must be inhaled for it to reach the receptors in the vomeronasal organ. In cats, the effects of nepetalactone can be moderated by several drugs acting upon the central and peripheral nervous system, and by several environmental, physiological, and psychological factors. The specific mechanism governing these behaviors has not been described."
http://science.howstuffworks.com/question303.htmSo there is scientific reason for a cats reaction to catnip. Thats how we know it. And we know catnip exists because we can see it and touch it and smell it. We can also detect it with instruments Now, if your argument is that you have some sort of god section of your brain..well..okay (but there isn't that much evidence for it, as far as I know). But that don't make god real...cause we can't detect anything by any other means. Your god is in your mind.
Plus, if you argue that you have a god receptor that I don't (and god exists) then that means that god purposefully doesn't want me to believe in god. Which makes god a dick.