Bubbles is King Kai's pet monkey, and he's basically the workout equipment of the North Kai's training regimen. During lessons, trainees have to chase him down as an endurance test—sounds simple until you remember they're doing it under 10 times Earth's normal gravity. Goku spent 40 days just trying to catch the little guy. Piccolo, on the other hand, grabbed him almost instantly after showing up for training in the afterlife (he'd been killed by the Saiyans and sent to Other World). King Kai wasn't thrilled about that—he complained that the test was meant to push Yamcha, Tenshinhan, and Chiaotzu, not a prodigy who'd spent an entire year getting stronger alongside Gohan while Goku was away.
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