The book I'm reading about the mysterious workings of the brain posits that sense experience is not linear. So the fact that dogs have 220 million olfactory receptors in their noses while humans have only 5 million does not mean that dogs smell a dirty sock at 44 times the volume that we do. What it does mean, according to the author, is that dogs' experience of smell is hugely more subtle than ours, separating out layers and shadings that humans can't begin to understand.

Walking through the graveyard this morning with my dogs and their sophisticated olfactory receptors, I smelled the most delicious aroma of autumn -- to my human nose, a combination of crunchy dry leaves and rich damp soil.

But the dogs were driven mad with joy by what they could smell -- squirrels, birds, last night's winos, beech trees and birch trees and oak trees, a dead decaying rat (which must have smelled gorgeous otherwise why roll in it?), foxes, other dogs who had recently passed by, other dogs who had not so recently passed by, a bit of a croissant deep in a tangle of brambles, a discarded sock, a KFC chicken bone (London's most common artifact) and presumably the aroma of the recent and long dead.

My metaphor-loving brain (another imponderable, according to the author) imagined showing a page of Dickens to the world's most sophisticated dog. He would see that the page was covered in strings of black squiggles that all look more or less the same. Words, we could explain to him. But to him they would be meaningless: generic, undifferentiated words.

When the same dog sniffs the air, however, he smells sentence after sentence, whole paragraphs and pages of plot -- including a long list of characters, actions past and present, intricate description, adjectives, adverbs, questions and answers -- an infinity of stories.

And I smell dry leaves.