What happened on 19 th septemberwith the Ghost?

The ghost received the final blow on the 19th of September. He had gone downstairs to the great entrance hall feeling sure that he would not be assaulted. It was about quarter past two in the morning and as far as he could ascertain no one was stirring. As he was strolling towards the library to see if any traces of the blood were left, he was ambushed by the twins to waved their arms wildly and shrieked 'boo' at the ghost, scaring him horribly.