There are many examples of free-standing (unanchored) objects or blocks which may start to rock if shaken. If the block is slender then overturning is a possibility. The stability of statues in a museum hit by an earthquake is a practical example. However, whether the block overturns or not (or slides, or bounces) depends very sensitively on the system parameters and initial conditions. This makes experimental repeatability very diĄcult, even in a carefully controlled laboratory setting. Extensive use is made of numerical simulation to support the experimental results and a variety of generic nonlinear behavior is described.