Just chew on a bit of blackboard chalk, a hundredth of the price and does the same job...I like a bit of pica eating me... makes a change from nibbling coal when in the bath...I had a bad paperback book nibbling issue for a while, quite common, and easy to spot what page you are up to...
or baking soda, half a spoon in a glass of water.
or baking soda, half a spoon in a glass of water.