Other source:
After Piccolo weakens Goku to where he can't lift any appendages (including the one arm his father made the mistake of leaving Goku). Piccolo flies to the sky like his dad, to finish off his nemesis. However unknown to Piccolo and the others Goku can fly and he uses the opportunity to headbutt Piccolo in mid-air for a ring out victory. Later Goku uses a sensu bean on himself and to revive Piccolo, not wanting to jeopardize Kami's health. Piccolo shows complete contempt for this, thinking Goku to be soft, and departs after vowing to defeat Goku.
