Miss Howard, said Poirot gravely, "this is unworthy of you." Suddenly she took her face from her hands. 
Miss Howard was crying because Poirot had caught her in a lie.
mnli hypothesis: Miss Howard was crying because Poirot had caught her in a lie. premise: Miss Howard, said Poirot gravely, "this is unworthy of you." Suddenly she took her face from her hands. 