Did you know your dog doesn’t just check the clock on the wall to know when you’re coming home? They don’t need to. They can smell exactly how much time has passed.

We live in a visual world, but our dogs live in an olfactory one. While we see the sunlight fading to know it’s evening, your dog is reading the “scent clock” of your home.

Experts suggest that dogs can detect the decay of odors. When you leave the house in the morning, your personal scent is strong. As the day goes on, your scent molecules slowly dissipate. Your dog learns that when your scent fades to a specific level—let’s say, 40% intensity—you usually walk through the door.

This is why they are waiting by the window ten minutes before you arrive. They aren’t psychic; they are smelling the specific “time” of the day based on the fading concentration of you in the air.

Next time your dog greets you, remember: they haven’t just been waiting; they’ve been counting the moments by every breath they take.