just beacuse you cant smell it... it has no smell??
have a read http://www.cannabisculture.com/node/8634
Dogs have about 25 times more olfactory (smell) receptors than humans. These receptors occur in special sniffing cells deep in a dog’s snout and are what allow a dog to “out-smell” humans. Dogs can sense odors at concentrations nearly 100 million times lower than humans can. Here’s a comparison to help you appreciate the vast difference in olfactory ability between humans and dogs: if all the sensory epithelia (skin tissue) in the average dog’s nose were laid out flat, it would cover an area of about 450 square feet, and contained within this nasal tissue are more than 200 million scent receptors, some 15 million of which have infrared capability. That means a dog can literally smell heat! If a human’s scent sensitive skin tissues were laid out flat, it would only cover about two square feet and contain less than five million scent receptors, none of which exhibit infrared capability. Also, in the brain of the average dog, more than 12 percent of the cerebral tissue is devoted to processing olfactory information. In humans, less than one percent of the brain is devoted to the same. Tests have proven dogs can detect one drop of liquid in a fifty-five gallon barrel of water, and some tests suggest dogs can even smell cancer cells.