This scene, in fact, transcends the film by moving you beyond the quotidian into the dream itself. As a character, Elsa Bannister exists in stasis rather than as action, as an ideal rather as a person. A White Russian born in Shanghai, she's another beauty with a past. She shimmers in white, symmetrical like a magazine model, hallucinatory like a spirit. She's a myth, the naughty lady from the gambling dens of the East, perhaps an entity who is pursuing the brooding O'Hara as a consequence of his accidental homicide in Spain.
Nothing is certain.
You are left to make associations, infer connections. In the noir universe, coincidence is Fate. Liam O'Flaherty published The Black Soul , a novel about a shell-shocked WW I vet who goes to convalesce on an island off the west coast of Ireland. O'Flaherty himself was a itinerant cosmopolitan very like Michael O'Hara, a merchant seaman who was familiar with the major seaports of the world. When Bannister goes to the seaman's hiring hall at the behest of his wife to find the man who saved her from the thugs in the park, O'Hara is seen using a typewriter.