"Dogs do that automatically. Human beings (with machines) have to cast around. It's slow. You might catch it, you might not catch it."
Secondly, relative to their level of sensitivity, dogs are very portable. "If you give me a room-sized station, I can probably develop something that can sniff as well as a dog," Coren says. "But portable? Um, no, I don't think so."
That's what makes dogs indispensable for police searches. Caissie estimates one dog searches more effectively than 10 officers.
"We can cover more area in less time," agrees Marty, one of CBSA's dog masters at the airport. He and Ozzie, a border collie cross, have made so many drug seizures that he doesn't want his last name used, lest those he has caught come looking for him.
Last year at Pearson, the CBSA made more than 760 drug seizures worth $140 million.
Still, the police and CBSA agree that machines and dogs both have their place in detection work.
"One can't replace the other. They're both very valuable tools," says Caissie.
The Toronto police also use devices such as portable X-ray machines for bomb detection.
Officers at CBSA say they use dogs and machines as independent tools that complement one another. And they're quick to point out that neither dog nor machine is much use on their own. It takes intelligent, well-trained humans to produce meaningful results.
Says CBSA superintendent Falzon, "The tools are only as good as the officer operating them."
For now, that's true, but the next step for machines is to make operators obsolete. Automation cuts out the expense of the operator and removes human error, says Elliott of Smiths Detection.
But, he adds, "I still to a certain extent think that machines will never replace everything, and I just have a sense that dogs may be one of those things."
Elliott recalls hearing recently about dogs sniffing out cancerous moles on human skin.
"Now how does that work?" he asks in a tone of awe.