Stanley Coren

The greatest fear dogs know is the fear that you will not come back when you go out the door without them.

Dogs don't know about beginnings, and they don't speculate on matters that occurred before their time. Dogs also don't know - or at least don't accept - the concept of death. With no concept of beginnings or endings dogs probably don't know that for people having a dog as a life companion provides a streak of light between two eternities of darkness.