The Bodhisatta was once a monkey living on a river bank. On his way from one bank to another, he used to jump off and on a rock in midstream, and a female crocodile, living in the river, longed to eat his heart and asked her husband to get it. So the crocodile lay on the rock, ready to catch the monkey as he jumped. The monkey noticing that, in spite of there being no tide, the rock was higher than usual, spoke to it and received no reply. His suspicions were then confirmed, and he said again, “O rock, why don’t you talk to me today?” The crocodile then revealed both his identity and his purpose, and the monkey resolved to outwit him. So he asked him to open his mouth, knowing that when a crocodile does this he shuts his eyes. So the crocodile did this, and the monkey jumped on to its back and from there to the other bank.
The story was related in reference to Devadatta’s attempt to kill the Buddha. J.i.278 f; cp. Kuruṅgamiga Jātaka.