Our border collie, Fly, is usually on duty at the stables. If the horses are in and waiting for their feeds sometimes one will bang their door with their hoof.

Fly runs to their door sits and barks just once, then another horse further up the row will bang its door, so off she goes to that one - sits and barks just once, then another .......... get the picture.
We're not sure if they are all playing the same game, or the horses are taking the p**s !

You may think well she's not that smart, but the thing is we've never taught her to do this. She's just worked it out for herself, that they shouldn't bank their doors !