"Masters and Students" (親子二代の荒修業 Oyako Nidai no Ara Shugyō, lit. "The Father and Son’s Harsh Training") is the two hundred tenth chapter of the Dragon Ball manga.
Piccolo attacks Gohan as part of their battle training. Gohan flies up at Piccolo with a kick, but Piccolo just holds it off with his hand. Gohan then dives at him with a punch, but Piccolo moves out of the way and then kicks Gohan from behind. Gohan says he couldn’t see him, and Piccolo says don’t look for him, but feel him. Gohan says that’s easier said than done as he dusts himself off, and so Piccolo blasts him with some eye lasers and yells at him that they only have six months. “Other than eating and sleeping, there’s only time for fighting me! Come on.” Gohan thinks he’ll die, so Piccolo tells him if that’s the case, get stronger than him and the Saiyans. Piccolo then strikes at Gohan, and tells him to defend himself better by focusing his ki.
Meanwhile, Goku continues along towards Kaiō’s place. It’s been six months, and he’s really exhausted and thinks it must go on forever. Then he finds the tail of the snake! But, there’s nothing here… But then he spots a little planet up in the air, and realizes Kaiō must be there. He jumps way up into the air to get a better look, and he spots a little house on the planet, so he must be there. But then he gets sucked right onto the surface of the planet. Goku wonders about the ground here, and thinks his body feels like lead. Goku then spots a little monkey, and thinks it must be Kaiō. He greets him and asks to receive training, and so the monkey starts dancing around with his hands in the air going “oohoohooh”. Goku thinks these weird movements must be the training, and so he starts trying to move around like the monkey. Goku tries to ask about the ground here, but the monkey just keeps making noises. Then someone asks Goku what he’s doing.
There’s a plump guy, with antennae, sunglasses, and a fancy dress outfit. Goku stops, and then asks the guy who he is. “I am… Mmm… Kaiyo… Kaio… Kaiō… I’m Kaiō!” Goku asks who the monkey is then, and Kaiō says it’s his pet, Bubbles. Goku had thought it was strange, and Kaiō says, “You’re the strange one.” Kaiō then asks if he’s come to hear his great new pun, and Goku doesn’t know what he’s talking about. Nevertheless, he tells it anyway. “Moshi moshi. Are? Daremo denwa ni… den wa!” (“Hello? Huh?… No one’s answering… the phone!”) Kaiō thinks it’s the greatest, but Goku doesn’t get it. Kaiō asks him what he wants, and Goku says to train. But Kaiō says to go home, he won’t train anyone who can’t laugh at such a great joke. Goku then bursts out laughing, and so Kaiō is pleased now. He says he’ll train Goku, so long as he passes the test — tell a pun that could make a “gag genius” like him laugh!
Goku freaks out, and Kaiō tells him he’d better go home if he plans on giving a weak joke. And then Goku blurts out, “Futon ga futton da!!!” (“The futon flew!!!”) Kaiō begins to chuckle, and so Goku has passed. Now Kaiō is prepared to teach him the greatest gags, but Goku says he’d come for martial arts. Kaiō tries to correct his arm placement, but Goku says it’s hard to move here. Kaiō asks if he’s from Earth, and explains that the gravity here is about ten times greater than Earth’s. So his body weighs ten times as much! He says to try jumping, and Goku can’t get much higher. Kaiō thinks that this will be fun.