Lockwood guesses at Heathcliff’s self-education in his absence.
sizar’s seat 
Earn honors by drawing blood refers to soldiering.
Making a fortune more promptly on the English highways refers to Highwaymen.

Note Cathy’s reception of Heathcliff, and the physical description of Heathcliff next to Linton harkens back to the soul comparisons of chapter nine; the physical mirrors the internal.

Notice that Nelly Dean is the voice of reason for Catherine. In a sense, Nell can be thought of as fulfilling functions of the Greek chorus.

“Good night — I’m an angel!” An angel of hell, maybe.

Do you feel Catherine is sincere in her warning to Isabella by describing Heathcliff, “an unreclaimed creature, without refinement, without cultivation; an arid wilderness of furze and whinstone” (89)? He’d crush you like a sparrow’s egg.

WH is a work that epitomizes atmospherics.  (When I was a kid in the sixties, by this time of 2017, science-fiction promised us transporters that would allow us to materialize elsewhere: I wish this were the case, and that we could take a field trip to these moors: the wind and the gritty mist and the roughness of gorse and the jutting stones would bring this home quickly to your skin and blood into the knowing.)

“You are worse than twenty foes, you poisonous friend” (90).

Nell attempts to corroborate the character assessment to Isabella, who will have none of it: we know where this is going, hey? One order of situational irony, coming right up: served hot, or cold?

“He is a bird of ill omen…Honest people don’t hide their deeds.”

Heathcliff looks at Isabella as if she was a centipede from the Indies, but soon notes “She’s her brothers heir, is she not?” (93). We guess at his motive, even if we do not recall Lockwood’s wondering how Heathcliff became landlord of the Grange and the Heights.