“What is the difference between the ‘birch’ mushroom and the ‘white’ mushroom?” —Anna Karenina

Now or never it must be said—that Sergey Ivanovitch felt too.
Everything in the expression, the flushed cheeks and the downcast eyes
of Varenka betrayed a painful suspense. Sergey Ivanovitch saw it and
felt sorry for her. He felt that to say nothing now would be a slight
to her. Rapidly in his own mind he ran over all the arguments in
support of his decision. He even said over to himself the words in
which he meant to put his offer, but instead of those words, some
utterly unexpected reflection that occurred to him made him ask:

 “What is the difference between the ‘birch’ mushroom and the ‘white’ mushroom?”

 Varenka’s lips quivered with emotion as she answered:

 “In the top part there is scarcely any difference, it’s in the stalk.”

Anna Karenina, Part Five, Chapter 5

 While at the Levins’ country estate, Sergey Ivanovitch, Levin’s
brother, falls in love with Varenka, Kitty’s friend from her European
trip. He, much older than she, is about to ask her to marry him. They
go mushroom hunting and repair to a glade, away from the others, where
he intends to propose.

 Sometimes the serendipitous occasion comes from not asking. We
can only wonder what would have come if he had proposed, but the book
is long, and maybe, as Kitty later on accepted Levin’s proposal, this
pair too will become a couple.