Fay sits in Frank's office and opens a book to read. She opens the book to a dog-eared page and seen from behind she turns the page. In the next shot from the front she turns the dog-eared page again.
When Lt. Hunter breaks through the floor he's knocked out by a heavy pile of falling debris that comes to rest on his head. Moments later when he regains consciousness and begins calling for help, the pile of debris has disappeared.