He had just had a wonderful idea about how to cope with the terrible lonely isolation, the nightmares, the failure of all his attempts at horticulture, and the sheer futurelessness and futility of his life here on prehistoric Earth, which was that he would go mad.

He beamed again and took a bite out of a rabbit leg left over from his supper.
He chewed happily for a few moments and then decided formally to announce his decision.
He stood up straight and looked the world squarely in the fields and hills. To add weight to his words he stuck the rabbit bone in his hair. He spread his arms out wide.
"I will go mad!" he announced.