A man is walking in the rain when a yellow leaf suddenly hops in front of him, startling him. His surprise is not really about the leaf: it interrupts him while he is mentally elsewhere. He has been reliving the image of his mother lying in a dim sickroom, her body tense with the will to die. The leaf jerks him out of that private darkness and back into the wet, busy street, where leaves, streetlamps, and traffic all blur together.
The mood is heavy and brooding, full of grief that sits just under the surface. The speaker seems caught between two worlds: the intimate, agonizing room where his mother is dying and the ordinary noise of the city. The leaf is a small, almost absurd trigger, but it shows how easily deep sorrow can be interrupted and then rush back.