The Quack Frog
A frog emerging from the mud of a swamp proclaimed to all the world that he was come to cure all diseases. "Here!" he cried, "come and see a doctor, the proprietor of medicines such as man never heard of before; no, not, Aesculapius himself, Jove's court-physician!"
"And how," said the fox, "dare you set up to heal others, who are not able to cure your own limping gait and blotched and wrinkled skin?"
Test a man's professions by his practice.