CHARADE.
Reading edition
If my first is my second, 'Tis sure to be fleet; If my second's my first, It is not fit to eat. And what is my whole Will depend upon whether My second and first You fit rightly together. If my second comes first, 'Tis an animal; but If my second comes second, Why, then, 'tis a nut. So if it's an animal, Then you may back it; But supposing it isn't— I leave you to crack it.