Chrysippus, a Greek philosopher from the third century B.C., is said to have recounted how a hunting dog arrived at a spot where three roads met. The dog smelled the two roads by which the quarry had not passed, then without hesitation or any further sniffing set off on the third. According to the philosopher, the dog had drawn a logical conclusion, reasoning that if the quarry had not taken two of the roads, it must have taken the third.
Facing a fork in a maze, mice often hesitate for a few seconds before continuing. Recent studies suggest that in order to decide which way to go, a mouse has to project itself into the future. We know that rodents replay previous action sequences in their hippocampus, so the wavering mouse in the maze probably compares the memory of old routes with imagined future ones. In order to do so, it will have to be able to tell the difference between experienced and projected actions, which requires a primal sense of self.