Another little line from an earlier book that becomes more significant later on

In CoS, after Harry, Ginny and Ron return from the Chamber, Dumbledore States: "Older and wiser wizards than [Ginny] have been hoodwinked by Lord Voldemort." Of course we already have Quirrell and Armando Dippet as examples of this at this point in the story. But arguably the most significant hoodwinking Voldemort does in the story is when he tricks Slughorn into telling him about horcruxes. That's what came to my mind when I read CoS this time around, anyway! I don't think this is foreshadowing, but it's another example of how JK had Voldemort's characterisation down from the very beginning.