 They ruled out that dogs simply went for any moving string, as in the dog–human trials the humans did not pull hard enough to make the other end move.They attributed success to the dogs' ability to read the social cue of their partner's behavior, but could not rule out that visual feedback of seeing rewards incrementally move closer also played a role.These results with pet dogs stand in stark contrast to the results with pack dogs, which in a study by Marshall-Pescini, Schwarz, Kostelnik, Virányi, and Range rarely succeeded in obtaining food.