When Lydia finds out about the video. She comes in, probably expecting a lecture from Lizzie about George Wickham, and she gets one, but not in the most gentle way. Lizzie thinks that Lydia agreed to the video, and knows about it. She's so mad at Lydia that she doesn't even assume Lydia doesn't know. Both Lizzie and Lydia receive a shock when Lydia discovers the video. Lizzie realizes that Lydia had no idea, and Lydia realizes that she doesn't know George Wickham at all. I thought this moment was more sad than Jane discovering that Bing left town. What Lydia discovers is mortifying and cruel. What Lizzie discovers is that she doesn't have faith in her sister at all.