Apparently he thought that a 'twat' was a nun's headdress.

'They talked of his having a Cardinal's Hat
They'd send him rather as soon an Old Nun's Twat.
The revelation restored my good humor, although it made it no easier to convince my standing man that he would find no soft, warm haven this night. Partly to induce him to lay down.....
I had a long row to hoe before I could plunge my spade into Melusine earth and plant seen there.
That is my standing man, Melusine.........You know his name. You must not fear him, for he loves you and only wishes for your pleasure. Come, make friends.