QUOTE : Lily blinked: she was surprised to hear Snape call her a “filthy little Mudblood.” She hadn’t been expecting it. Snape could not endure being told that he owed his relief to Lily’s willingness to put herself on the line for him. We don’t see in this memory how well they know each other, but her surprise shows that it’s something that hasn’t happened before. The betrayal causes enough of a change in her attitude that she calls him by the same name that the bullies do and makes her own sexually humiliating observation.