King Sāma of Benares had a state horse Pandava, whose trainer was the lame Giridanta. Observing that his trainer limped, the horse imitated him. When the king saw the horse limping, not being able to discover the reason, he asked his adviser, the Bodhisatta, to investigate the matter. The Bodhisatta reported that it was the result of evil association, and had the trainer replaced by another. The trainer was Devadatta (J.ii.98f).
For the introductory story see the Mahilāmukha Jātaka.