the scene where the book describes how Rodrick and his are lovers and that they are married to each other. this is also when the book describes that the fact that their family tree doesn't have many branches.
This scene is when the narrator decided to stay in the house of the ushers for 7 days and is insane for staying in that house after seeing all bad things that happened.
This was when Rodrick's wife/sister was found coming out of the basement after everyone thought she was dead. The scared was so bad it killed Rodrick and his wife/sister.