Cannonball: Experiment 520

A bird has discovered a strange blue ball in her nest. After deciding she doesn't need it, she discards it into the river running below her tree. It turns out it's #520's pod, and it activates. Now the experiment is wreaking havoc over the island with it's huge behind by bouncing and shaking the ground. So, Lilo and Stitch must capture it, but Gantu is on it's trail too.