I don't think they know. Mine don't at least. But if I'm gone for more than a day they do figure it out, just not right away. I'll pray Gaia will be fine. Smokey stops eating when we leave him as well but he doesn't let himself starve. Zeeva blows her coat like none other, paces, and continuously knocks down the barrier from the stress. But in the end both are happy to see me and all goes back to normal.
A dog's smile is on his butt! c: