"A Farewell to Arms" (解けた怪物の謎 Toketa Kaibutsu no Nazo, lit. "The Mystery of the Monster Solved") is the one hundred sixty ninth chapter of Dragon Ball Z and the three hundred sixty-third overall chapter of the Dragon Ball manga.
As the Creature prepares to fire a Kamehameha, Piccolo is shocked, wondering how it knows the move. The Creature unleashes his blast, and Piccolo is surprised to see that it is indeed a Kamehameha. He manages to dodge, leaping into the air. The monster, however, ambushes Piccolo and grabs him from behind, pinning his arms and legs. It says that he has him now, and stabs Piccolo in the arm with his tail. He manages to suck energy from Piccolo's arm before the Namekian headbutts him and escapes. Piccolo's right arm, however, is now withered and useless. The Creature and Piccolo land, and It tells Piccolo that he cannot defeat him with only one arm.
Piccolo agrees, saying that he cannot compete with it in his current state, and that It has won. The Creature praises Piccolo's sensibility, and says that his initial evolution will be nearly complete after he absorbs Piccolo's life force. Piccolo asks the Creature to tell him how he has Goku and Frieza's kis and knows the Kamehameha. It decides to grant what he considers a meaningless last wish, and reveals his name to be Cell and the fact that he is an artificial life form. He says that he was created by Dr. Gero's computer, after the doctor experimented with combining cells from great fighters. He reveals that although Gero abandoned the experiment, the computer never gave up, and harvested cells from Goku, Piccolo, and Vegeta three years before for the project. Piccolo says that Cell's Kamehameha was weak because the cells used from Goku were three years old. Cell continues on, noting that samples were taken from Frieza and King Cold when they came to Earth, but that cells from Future Trunks were not used because the computer had enough Saiyan samples. This does, however, explain why Cell's ki is identical to Goku and the others.
Piccolo asks how the cells were harvested, and Cell tells him about the small spy robots that followed their every move and scraped their cells. He points out the presence of one right there, and Piccolo angrily destroys it. Cell says that it is too late, and that the research has been done. Piccolo tells him that Dr. Gero's Lab was destroyed, but Cell says that the computer was in the basement. Piccolo asks why it took Cell three years to come back in time, and Cell explains that he needed three years to mature from his egg form. Piccolo then asks why Cell came back in the first place, and Cell explains that he needs to absorb Android 17 and Android 18 to reach his perfect form, but somehow Future Trunks had defeated them in his time. He says that he stole Future Trunks' Time Machine and came back to the past, to a time that Future Trunks had already programmed in. All Cell had to do was push a button. Piccolo, understanding everything so far, theorizes that the Trunks from Cell's timeline figured out a way to destroy the Androids, and intended to travel back again to tell them how to destroy them. Cell then says that when he is complete, he will have unimaginable powers, and Piccolo asks why he wants so much power. Cell replies that he was created to be the most powerful being in the cosmos. Piccolo then thanks Cell for answering his questions, and rips off his withered arm. He quickly regenerates a new one, stunning Cell. Cell asks if the questions were a trick just to keep him talking, and Piccolo says that Cell should have known about his regeneration, since he has Piccolo's cells.