Answer:
He realizes his nausea is due to the drug, not simply the cigarette.
Step-by-step explanation:
Classical conditioning is a phenomenon that is being widely used in psychology and was developed by Ivan Pavlov when he was trying to experiment with the dogs. Ivan Pavlov described classical conditioning as a learning process that involves a particular "biologically potent stimulus" that is being paired or associated with a formerly unlearned or neutral stimulus.
Classical conditioning is also referred to as respondent or Pavlovian conditioning.
Henry experiences trouble quitting the cigarettes as he was getting associated with nausea and drug but not nausea and cigarettes.