This seems highly unlikely, but in the final duel, Voldemort says that when Lily had died, Snape told Voldemort that there were other women of purer blood. My question is- when? He did not talk to him until Voldemort's return, right? (for reference, see American Version of DH, page 740) If so, why would Lily have come up in conversation? True, Voldemort thought Snape had left him forever (probably because of Lily), so just how did Snape convince him he hadn't?

This seems like too simple of an answer really at first, but it just confused me. I appreciate any responses.