I heard about a test someone did, after wondering how their dog was always standing in the window at the end of each workday, anticipating their owners arrival home. After casting about, a theory was developed that the dog "smelled time". That is, as the day wore on, the scent of their owner, decreased in the air; at a low-enough concentration, the dog knew it was about time for the front door to open and their owner to arrive home.

To prove the theory, someone went to the owner's work at noon-time, and gave him a new shirt, collecting the one he'd been wearing for half a day. They took that worn shirt, and swirled it through the air back at the house; recharging the owner's scent in the air. The dog was asleep and away from the front door, and surprised when its owner arrived home at the normal time.