SUBREDDIT: r/dogs
TITLE: [Fluff] How does my dog read a calendar?
POST: I work from home and most days my chihuahua sits quietly by my desk.  She's not a yapper in general.  Only goes to bark at the door if someone approaches.  She's lazy.

Every other week a maid comes. She loves to follow the maid around and bark at her.  When I get up and start tidying up that morning, I know she can figure it out. Maid is coming.  So she barks at EVERYTHING outside thinking they are pulling up.  I figured she could sense my hustle getting things ready for the cleaning.

This morning I did not do that routine, yet she is still perched at the window and barking at any car that goes by. I have given NO cues today.  How does she know?

The only thing that happened was my husband threw the sheets into the wash before he left for work, but we wash the sheets at other times, not just when maids are coming, but only in the early AM when maids are coming.  Could that tiny thing set her off? And how would she know sheets vs. normal loads of laundry?

Otherwise, she must have a clock inside her.  The other thing is that the street sweeper comes today and she may have heard that and knew the maids come on the same day -- but they only come twice a month and street sweeper is weekly, and on other Wednesdays she does not act like this.

Any other stories about dogs unique ability to read time? I can understand them knowing a 24 hour clock based on the sun and their stomach growling and they know it's time to eat - but every two weeks? How on earth could she know?  I got up and have been sitting at my desk -- any other day, she lays in the dog bed next to me.  She's at the couch looking out the window waiting and  barking.
TL;DR: 
My dog knows the maids are coming today and there have been NO clues tipping her off - how does she know?