Other source:
Captain Ginyu prepares his revenge by switching with Piccolo, but Gohan is able to throw Bulma (as a frog) in the way to get her body back. Meanwhile, Goku is being beaten up by Frieza with his power increase and even the Kaio-ken attack doesn't work. But as he is held by the monster's power, he has a vision showing what Frieza could do to Earth. Rocked and inspired by the vision, Goku powers up.
