It's there that Alecto Carrow spots Harry and touches her Dark Mark, letting Voldemort and the rest of the Death Eaters - including Snape - know she has Potter. Among the changes: In the book, Luna brings up the lost diadem of Ravenclaw and takes Harry to the common room to show him what it looks like on the statue of Rowena (Cho offered, but Ginny suggested Luna do it).