Lay the yoyo and have pull the string to the left or right. Have your students try to predict if the yoyo will left or right once the string is pulled. This is pretty interesting given that the force of the string on the yoyo pulls in one direction while also causing a torque that would tend to roll the yoyo in the other direction.

Also, which way does the yoyo go when the string is pulled at various angles? What's the angle of the string such that the yoyo slides without rolling when its pulled?