Inflatable ball with unpredictable movement

An inflatable ball comprising:

• an inflatable outer chamber formed of an air tight flexible outer skin which, when inflated, defines an interior volume;
• a hand grip molded as a unit with and extending radially from said outer skin whereby a child may sit upon said ball, when inflated, and roll or bounce on said ball while maintaining seated contact therewith;
• a sealed inner chamber filled with a substance substantially heavier than air and occupying a relatively small amount of said interior volume;
• a plurality of elongated elastic members radially extending and evenly spaced apart in all three dimensions, each elastic member of said plurality connected to, and extending between, said inner chamber at one end thereof and to an inner surface of said outer chamber at another end thereof;
• said plurality of elastic members cooperatively sized in length and suitably tensioned, when said outer chamber is substantially fully inflated, to support and hold said inner chamber centrally in an at-rest position within said interior volume;
• each of said plurality of elastic members cooperatively stretching and contracting within said interior volume in response to movement and impact of said ball causing said inner chamber to be unpredictably displaced from the at-rest position by gravity and inertia resulting in erratic movement of said ball.