You were born, I suppose, at Little Witham. A reproof to a noodle. The pun, of course, is on little wit. Witham is in Lincolnshire.
“I will be sworn she was not born at Wittham, for Gaffer
Gibbs says she could not turn up a single lesson like a
Puns of this sort are very common. (See Bedfordshire, Nod, Dunce, Cripplegate, Shanks' Nag etc.)