"It Only Gets Harder" (亀仙流の厳しい修業 Kame senryū no Kibishī Shūgyō, lit. "The Kame-sen School’s Tough Training") is the thirty-first chapter of the Dragon Ball manga.
The chapter opens with Goku and Krillin working in a field. Roshi tells them they cannot use the hoes they are currently using, but they must use their hands. After a short while, the two are finished, and they go off to eat breakfast.
Once they finish their breakfast, Roshi sits them down and tells them they must train their minds, as well as their bodies, to become master martial artists. He asks Goku to start reading, who, surprisingly, know how to read perfectly.
At 12:30 PM, they decide to take an hour nap. After finishing their nap, they begin construction work, which they finish in minimal time. Once that is complete, the boys are to swim for their training. Fed up with training, Goku asks Roshi to teach them how to fight. He tells them he cannot unless they can move a large boulder beside him. When Krillin doubts that such a feat is possible, the hermit quickly demonstrates that it is. After telling the boys that they can do this too if they train everyday, Goku easily moves it (even farther than Roshi). To cover up this embarrassment, Roshi lies and says that's the wrong rock, and a much bigger rock, one that Goku cannot move, is the real one. As they ask for him to move it, he tells them to go back to their training, implying that he cannot move it himself.
When they return to the lake, Roshi instructs the boys to swim to the other side of the lake and back ten times. However, there is a shark in the lake, but the two manage to pass the test.
For their next segment of training, the two are tied to a tree, which has a beehive on it. After Roshi hits the hive, dozens of bees swarm the boys.
Once back at Kame House, Roshi tells the boys, who have welts all over their bodies, that their training for the day is over. Krillin asks if they are gonna train like this everyday, which Roshi replies to with a yes. As the chapter ends, the hermit gives the boys twenty pound Turtle Shells to wear, which causes Krillin to fall over.