The Vicar is Coming to Tea and One Hundred and Twenty-seven Other Warnings of Social Embarrassment.
This is a treatise on the subtle signals that may be used between married couples or other intimates to warn against some current or imminent social transgression or faux pas. Some of these were in evidence at a dinner party at Crundells when Sybil mentioned to Sam a letter from Mrs. Wainwright (meaning "put a sock in it or you'll be sorry") while Col. Charles Augustus Makepeace missed a signal from his wife. She complained as they left that "you had the stable door open all evening".
Author: Dr. Bentley Purchase, published by Unseen University Press.
An informal variant or two occur in the dinner at Ramkin Manor, described in Men at Arms.
Willikins, I don't think Captain Vimes wants any wine. said Lady Sybil. Sybil is also capable of some very loud non-verbal communication of these delicate social warnings.