Table 1.

List of the hypotheses and predictions

	Predictions
	Persistencea	Latency and frequency of looking back when manipulating the impossible bowl	Overall duration of looking back
1. Looking back is a problem-solving strategy
1a. Domestication has selected in dogs the tendency to look at the human, which favoured the development of looking back as a problem-solving strategy	Pd should be less persistent in the social condition than in the control conditions and less persistent than FRd in the social condition	All subjects should look back sooner and more frequently in the social condition than in the control conditions but Pd should look back more frequently after attempting the impossible bowl than the possible bowls	All subjects should look longer at the human than at the objects, but Pd should look longer at the human than FRd
1b. Domestication did not have a selective effect on dogs’ tendency to look at the human but looking back represents an acquired problem-solving strategy	Pd should be less persistent in the social condition than in the control conditions and less persistent than FRd in the social condition	Pd should look back sooner and more frequently in the social condition than in the control conditions and more frequently after attempting the impossible bowl than the possible bowls. FRd should look back with similar latency and frequency in all conditions	Pd should look longer at the human than at the objects and should look longer at the human than do FRd. FRd may look longer at the human than at the object due to the higher saliency of the human or they may not look at the human at all
2. Looking back is not a problem-solving strategy
2a. Looking back is only driven by the dogs giving up and then looking at the most salient object	Subjects should be equally persistent in all conditions	Subjects should look back with similar latency and frequency in all conditions	Subjects should look longer at the human than at the objects and longer at the human shape than at the cardboard. Pd should look longer at the experimenter than FRd due to their stronger relationship with the humans
	No differences between pet dogs and free-ranging dogs
2b. Domestication has selected in dogs the tendency to look at the human face independently of the situation	Subjects should be equally persistent in all conditions	Subjects should look with a shorter latency and more frequently at the human than at the objects but with similar frequency after attempting the impossible bowl or the possible ones	Subjects should look longer at the human than at the objects and longer at the human shape than at the cardboard
	Overall no differences between pet dogs and free-ranging dogs

Pd pet dogs, FRd free-ranging dogs

^aPersistence refers to the total duration of interaction with the impossible bowl