What insight does juror 8 make about the 3rd jurors anger regarding the defendant?

After a bit of provocation, the 3rd Juror becomes angry with the discussion in the room. 8th Juror calls him a “self-appointed public avenger” and a “sadist,” and 3rd leaps at him. Restrained by the other men, he shouts, “God damn it! I’ll kill him! I’ll kill him.” 8th Juror asks, “You don’t really mean you’ll kill me, do you?” proving his earlier point about how people say, “I’ll kill you,” when they don’t really mean it.