In Man Handing a Letter to a Woman in the Entrance Hall of a House (1670) by Pieter de Hooch the dog's white nose 'is in a direct line to the girl who is standing between shadow and light and pointing the way out. It could be looking at her as if nothing were happening. But it isn't. It is looking over its shoulder at the shadowed space where the painter is standing and from which we too are looking through the room to the threshold of the brightly lit courtyard.... Meanwhile, as the girl and the dog are starting to respond to the entrance of the messenger, the little dog  on the woman's lap has already noticed him.' Here at the Rijksmuseum website is this beautiful painting in more detail.