Horses prefer to solicit a person who previously observed a food-hiding process to access this food: A possible indication of attentional state attribution.

Inferring what others witnessed provides important benefits in social contexts, but evidence remains scarce in nonhuman animals. We investigated this ability in domestic horses by testing whether they could discriminate between two experimenters who differed in what they previously witnessed and decide whom to solicit when confronted with an unreachable food source based on that information. First, horses saw food being hidden in a closed bucket (impossible for them to open) in the presence of two experimenters who behaved identically but differed in their attention to the baiting process (the "witness" experimenter faced the bucket, the "non-witness" faced away). Horses were then let free with both experimenters, and their interest towards each (gaze and touch) was measured. They gazed at and touched the witness significantly more than the non-witness (n = 15, gaze: p = 0.004; touch: p = 0.003). These results might suggest that horses inferred the attentional state of the experimenters during the baiting process and used this information to adapt their later behavior. Although further study would be necessary to conclude, our study provides new insight into attentional state attribution in horses and might hint to the existence of precursors of a Theory of Mind in horses.