Why Is Your Dog Laughing?

Wesson decided to take a closer look. But it's difficult to study two animals interacting, because they must be wired to sensors and computers and all those wires would become entangled as they rolled around on the floor.

So Wesson teamed up with a computer expert and the two developed a wireless system using today's near-microscopic technology. A sensor was placed in one nostril in each of two rats, and linked wirelessly to a receiver and computers. The sensor detected each sniff.

Four million sniffs later, Wesson had his answer. One of the rats clearly outranked the other, and that rat sniffed quickly and furiously until the subservient rat reduced its sniffing and backed away.

The message was clear: Sniffing was a form of communication that had nothing to do with detecting odors. A subsequent experiment proved that. When the rats were fed oxytocin, the so-called "love hormone," the animals didn't sniff at all, and there was no sign of aggression. The rat with high status apparently forgot to sniff, so the sniffing clearly was a form of communication that no one -- except the rats -- knew was there.

This finding fits nicely with a discovery in the 1970s that rats also communicate through vocal ultrasonic frequencies, which we can't hear.

But sniffing may turn out to be even more important. In the canine world, odor is king. Dogs have a sense of smell that is vastly superior to humans, and when your pooch sticks his nose into another dog's business he's picking up a lot of information, from the other dog's health to his diet to his gender. And probably stuff we don't even know about.

We humans don't do that, of course. At least not overtly. But the multibillion dollar perfume industry is banking on the fact that to humans, smells matter. Our recent predecessors probably depended a lot on smelling.

No less an authority on human evolution than Paul Ehrlich, the president of the Center for Conservation Biology and Bing Professor of Population Studies at Stanford University, suggested recently that we would probably still be sniffing each other if we hadn't changed to walking upright.

By the way, one reason we don't speak the same language as our pets is we don't want to. We want them to learn ours -- which to a degree they do -- and we actively suppress some of their attempts to communicate. As in "don't bark."

That's what a dog does.

But back to rodents. One experiment from a major university, published in a major science journal last year, sought to prove that rats have empathy -- the care among most humans for others that is so intense we do more than sympathize, we actually feel their pain.

One rat was constrained in a trap while another wandered freely around the pen. The trapped rat was suffering so much that the free rat finally figured out how to open the trap and set it free. Thus, rats have empathy.

Maybe the trapped rat promised to lead the free rat to a secret stash of peanuts. Then it wasn't empathy. It was bribery.

But of course we will never know because nobody there interviewed the rats.

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