How we cite our quotes: (Part.Chapter.Paragraph)
Quote #7
"Now I think of it," said Mr. Riderhood, evasively, for he was substituting those words for "Now I see you so jealous," which was the phrase really in his mind. (14.11.89)
Riderhood knows that Headstone is motivated by jealousy. But he's a crafty enough dude to manipulate Headstone by playing on his emotions.
Quote #8
"Let him look to that […] Let him look to that! It will be bad for him when men he has injured, and at whom he has jeered, are thinking of getting hanged." (16.1.42)
Eugene doesn't really know how much he's playing with fire when he constantly insults and makes fun of Headstone. He doesn't realize that Headstone is willing to risk execution if it means shutting Eugene up once and for all.
Quote #9
"You've seen him with her!" exclaimed Riderhood, starting up.
"I have." (16.1.90-91)
Well that just about does it. Headstone has seen Lizzie Hexam walking alone with Eugene Wrayburn… which in Dickens' time was as bad as making out. The gloves are coming off, and it's probably around this time that Headstone decides to murder Eugene.