Learn how to read minds. Amaze your friends with speed calculations and different funny maths tricks. Play the specially designed math memo card game with your audience. Calculate included. Warning! Contains button battery. A button battery can cause serious injuries if swallowed or placed inside any part of the body. Keep batteries away from children whether new or used. Dispose of used batteries immediately. If you think that batteries might have been swallowed or placed inside any part of the body, seek immediate medical attention.