The narrator rebukes the idea that the mark on the wall can be defined, philosophizing about its nature and the nature of life, more generally. This long, stream of consciousness contemplation becomes situationally ironic when someone interrupts the narrator's train of thought at the end of the story, revealing that the mark is a snail:
'It's no good buying newspapers . . . . Nothing ever happens. Curse this war; God damn this war! . . . All the same, I don't see why we should have a snail on our wall.'
This twist at the end of "The Mark on the Wall" is a good example of situational irony: the reader expects that the mark's identity will remain a mystery. The narrator herself seems to revel in this mystery, asserting that "nothing is proved, nothing is known." Indeed, the multivalence of the mark—its ability to simultaneously represent everything and nothing—is a crucial part of the philosophy Woolf explores in "The Mark on the Wall." Life, she argues, is a series of mere coincidences that have meaning because people assign them meaning. The world is what one makes of it; and the mark, in this philosophy, is whatever the narrator needs it to be.
Ironically, the narrator never considers that the mark might be a snail until someone else offhandedly and anti-climactically identifies it as such. The narrator's external reality contradicts her internal philosophical musings, a truth that Woolf reveals abruptly, cutting short the stream of both the narrator's and reader's consciousness.
