A book of this sort is totally impossible to tell from a normal one, although if a detect magic spell is cast, there will be a magical aura noted. Any character who opens the work and reads so much as a single glyph therein must make 2 saving throws versus magic. The first is to determine if 1 point of intelligence is lost, the second is to find if 2 points of wisdom are lost. Once opened and read, the vacuous grimoire remains, and it must be burned to be rid of it after first casting a remove curse spell. If the tome is placed with other books, its appearance will instantly alter to conform to one of the other works it is amongst.If I ever publish a fanzine, I'm calling dibs on The Vacuous Grimoire as its title.