My little Jack Russel Charlie is confusing the crap out of me

Our postie doesnt arrive the same time everday but every day 15 minutes before he pops the letters through the letterbox he starts growling quietly to himself in anticipation

How does he know hes on his way ?

The postie arrives on foot so its not as if he hears a van passing etc

Also, he doesnt do it on a sunday because theres no post. I just presumed he counted the days.

But, during the xmas holidays theres obviously been no post on certain days during the week ? He hasnt started the his usual ritual of growling

How the feck does he know the posties not coming ????????????????

few piccies of the little mite;