Mr. Pneumonia (Metaphor)
Though pneumonia is an illness, O. Henry personifies it in the story, using metaphorical language that compares the illness to an invisible stranger who mercilessly stalks the streets of New York and strikes down victims with his "icy fingers."
Mastiff-In-Waiting (Metaphor)
When describing Behrman, the narrator notes that the old man thinks of himself to be "especial mastiff-in-waiting to protect the two young artists in the studio above." In this metaphor, the narrator is comparing Behrman's fierce loyalty and protectiveness to that of a mastiff, a large dog.
Fragile as a Leaf (Simile)
When Sue visits Behrman, she tells him about Johnsy's condition, and reveals that she fears Johnsy will float away, since she is "light and fragile as a leaf herself." In this simile, Sue compares Johnsy's fragility to that of a leaf, suggesting that she is just as vulnerable as the ivy leaves.
