Sentence 1: John bought new headphones. 
 Sentence 3: John returned his defective headphones 
 Sentence 4:  With the money he got, John bought a better pair of headphones 
 Sentence 5:  John enjoyed his new, functional headphones 
 Option 1: John ignored that the headphones he sold were defective. 
 Option 2: John noticed that the headphones he bought were defective.