This is a "sliding board book" and there are six sliding boards including the one on the front cover. A sliding board in this case means the book pages are composed of several layers of card stock so thick that an open pocket in six of the pages has been formed, inside of which another piece of substantial cardboard can be moved back and forth. There are thumbnail cut-outs on each side of the slider that make moving it back and forth very easy. By moving the slider from one side to the other, it is possible cover or uncover additional animals. Thus, "I see one cow. He says 'moo!' Add one more (move the slider to the other side) and you get TWO," continuing on to ten. This sturdy little 5" by 7" book packs a lot of fun and learning. Beginning with the tactile pleasure of moving the slider, through the educational experience of actually adding animals hidden under the slider and counting them; and, additionally, the possibility of being able to subtract animals as they disappear back under the slider, makes this book a winner. 2004, Little Simon, Ages 2 to 4.