The ideal gas law states that the external pressure, P, is inversely proportional to the volume, V, and directly proportional to the number of moles of gas, or PV/n = constant. This means that if the external pressure decreases (with a fixed n), the volume of gas will increase. In a vacuum chamber, the volume of the balloon would certainly increase because P is less. Whether or not the balloon actually explodes depends on how low the pressure attainable by the vacuum chamber is and the elasticity of the rubber. If the material of the balloon is very strong, then it would be more difficult to expand and the balloon may not explode. If the balloon is filled to capacity, there is a greater chance that the balloon will explode since the change of volume will cause increased strain on the balloon material. If the size of the chamber is very small, then that might make the balloon less likely to pop since the balloon might expand to make contact with the walls of the vacuum container which would act as an increased external pressure on the balloon. This would not let the balloon expand any further, thus making it less likely to pop. There is not much difference if the balloon was made into an animal with two or more pieces. What would first happen is the parts of the animal would disappear and the balloon would turn into a single round section. This is because as the balloon expands, the knots in the balloon would unravel to allow for the balloon to stretch even further.