It's no secret that a dog's sense of smell is much, much more sensitive than that of their human companions. That's just part of what makes them such invaluable companions to law enforcement officers and search and rescue teams, but every household dog -- a guard dog in their own right -- has the same superhuman ability to not just smell, but process the information they receive.

Smells are detected by olfactory receptors in the nose. A human has about 5 million of these receptacles in their nasal passages, while a dog has about 220 million. Receptacles aren't just in the dog's nose, but continue throughout their nasal cavity and are even found on the delicate bones and membranes within the nasal passages. The portion of a dog's brain that processes information from smells is also more highly developed than a human's, allowing the dog to better interpret the information that their nose is giving them.

In addition to more highly sensitive organs, dogs also have some extra structures that humans don't. The vomeronasal organ, or Jacobson's organ, sits alongside a dog's nasal passages and mouth. These sacs are filled with a fluid that contains still more scent receptors. It is believed that this is the organ that also allows dogs to distinguish different types of pheromones in addition to the same kinds of scents and smells human can recognize.

Ever taken your perfectly calm and collected dog somewhere, and all of a sudden she's concerned or afraid when nothing seems to have happened? It's possible that she's smelling the trace remnants of something that may have happened before -- and this can be as simple as the passage of a fearful dog leaving pheromones yours is now detecting and understanding as a reason to be afraid. The last dog there was afraid, so in her mind, she should be, too. That's the effects of pheromones.

It's also estimated that about 33% of the information that's processed by a dog's brain is received from their sense of smell. This means that your dog's behavior isn't just based on what he or she is seeing, but it's also based on what they are smelling -- and these smells are often way beyond your abilities to detect.

One of the most obvious examples of smelling behavior is when two dogs meet each other. Their first instinct is to sniff each other, completely and thoroughly -- sometimes to the embarrassment of their owners. Even if they know each other well, the behavior is still there. Why?

Dogs aren't just using their sense of smell to identify each other -- their ability to smell is so efficient that they most likely know their buddy is just around the next bend before you do. They're seeing where the other has been, what kind of mood they're in and what kind of pheromones they're giving off -- along with what they've recently rolled in. It's the equivalent of the conversation that's taking their owners a much longer time to communicate.

Of course, this is also the same sense and ability that has made dogs invaluable companions to law enforcement and search and rescue teams. Depending on what the dog's job will be, they can be taught to recognize, identify and point their handlers to certain types of smells. Drug dogs can find even the smallest traces of narcotics, while bomb dogs can easily scent components disguised as something else. And search and rescue dogs can scent a person that has passed through an area hours ago, or find even the smallest remainders of a body.

And contrary to popular belief and the wisdom of television and movies, water doesn't even entirely destroy smells for dogs. Some search and rescue dogs are trained specifically to detect smells in water; gases can rise to the surface, along with hair, blood and skin particles. All these register loud and clear for canines, allowing them to help find drowning and accident victims that have been completely submerged.

All dogs have this almost supernatural ability to smell and process the information they receive, although some breeds are more likely to be used as working dogs because of other factors. German shepherds are a popular companion for law enforcement because of their strength, intelligence and loyalty, while working in harsh or cold conditions can give hardy, double-coated dogs like shepherds, golden retrievers and border collies a distinct advantage.

So the next time your dog goes into the kitchen looking for the steaks you know were cooked last night, don't be surprised. For him, the mouth-watering aroma is still filling the air.