This is an excellent question, and I think we just don’t know. But we do know that the five senses we do know about are very well attuned, and in my observations there is a combination of extremely developed abilities that help dogs perceive things we don’t, but we see the ‘uncanny’ results - like knowing we’re coming home long before we think they could hear the car, or knowing if a visitor is a friend before they’ve walked up the garden path. I’m sure this is a combination of highly attuned senses, plus other things we just don’t notice like routines, weather, and chemical smells associated with eg fear or illness. It’s fascinating!my question is, how does she know who's going past? She has never made a mistake about who has been there, to my knowledge. Can dogs smell through glass, and at that distance?