The Tern. The Turnip.
Reading edition

To tell the Turnip from the Tern, A thing which everyone should learn, Observe the Tern up in the air, See how he turns, and now compare Him with this in-ert veg-et-able, Who thus to turn is quite unable, For he is rooted to the spot,
While as we see, the Tern is not: He is not always doomed to be Thus bound to earth e-tern-ally For "cooked to a tern" may be inferred, To change the Turnip to a bird.

Observe the Turnip in the Pot. The Tern is glad that he is not!