Watching Sunset(S03E06) and Walt is reading the copy "Leaves of Grass" when Hank calls him to ask of Jesse's whereabouts. He tells Walt Jesse is now selling Meth, using an RV as a roving laboratory. This of course allows Walt to get ahead of the situation, ultimately making Hank believe Marie has been in a car accident so they have enough time to destroy the RV.
Also in the same episode Gale quotes a poem to Walt.
When I Heard the Learn'd Astronomer by Walt Whitman:
When I heard the learn'd astronomer,
When the proofs, the figures, were ranged in columns before me,
When I was shown the charts and diagrams, to add, divide,
and measure them,
When I sitting heard the astronomer where he lectured with
much applause in the lecture-room,
How soon unaccountable I became tired and sick,
Till rising and gliding out I wander'd off by myself,
In the mystical moist night-air, and from time to time,
Look'd up in perfect silence at the stars.
Amazing, how things come around in this show.