A more practised physiognomist would have been able to interpret that look. It was the one that butlers always wear when they have allowed themselves to be persuaded against their better judgement into becoming accessories before the fact in the theft of their employers' pigs.
In P.G. Wodehouse's "Summer Lightning," the narrative features a keen observation of a butler's expression. This look symbolizes a conflict of loyalty, as it reflects the butler's internal struggle when he has yielded to temptation, going against his better instincts. The moment reveals the complexities of human nature, particularly in situations where duty and personal interests collide.
The phrase suggests that an expert in reading facial expressions, or physiognomy, would recognize this telltale sign of guilt and complicity in unethical behavior. It emphasizes the butler's role in the deception of his employer regarding the theft, highlighting themes of betrayal and moral quandaries within domestic settings.