Why dogs stick their heads out of car windows

For dogs too, getting out and about excites their wild senses. And for such intelligent animals, you can't beat a road trip. While we are obsessed with visual landmarks, they focus only on scents. We have a measly six million smell receptors, but a dog's nose contains 300 million.

They use it to unravel stories about the world around them. Predictably, most are about food. 

Forty times more of their brain than ours is devoted to deciphering smells.

They home in on those with special significance. A single chemical aldehyde found in blood makes this one-time hunter drool.

There is a way to bring their smelly world to life. Schlieren photography visualises the air currents that carry odours and shows the remarkable workings of a dog's nose. Dogs breathe out through the side slits in their nostrils. As the expelled air rotates, it helps draw more scent into the nose. This two-way current helps a dog gather scent almost continuously. But that's not all. 

A male can smell a female in heat at concentrations of one part in a trillion.

Licking helps capture more of her alluring scent. His tongue takes the odour to a second smell organ in the mouth, hardwired to the brain and tuned to these sexual pheromones. It's love at first sniff.

For dogs, being a passenger rivals any wild experience, but it can be tinged with disappointment too.

The streets of Paris may be full of romantic promise, but pet dogs are seldom in control of their destiny.

Love may be in the air, but it's so rarely fulfilled.

© BBC