Why a dog is man's best friend.

[Dirt]

http://www.cnn.com/2009/LIVING/wayoflife/03/27/mf.dog.sniffing/index.html

Damn good noses.

[Bahimiron]

Looks like someone just read Stanley Coren's How Dogs Think. In the chapter on their sense of smell he mentions pretty much every one of those examples.