D left his horse and van unattended in a crowded street and went to see his friend in the adjoining street. While D was away, a dog barked and pounced on the horse. The horse got frightened and started running furiously along the road with the van. P, a pedestrian, saw X in danger of being run over and in order to save him pushed him away, but in doing so, he himself was injured. P sues D for damages: