"Impetus…!!" (きっかけ…!!, Kikkake…!!) is chapter 151 of the original Naruto manga.
A few days after beginning his Rasengan training, Naruto reflects on his lack of progress in popping the water balloon. Jiraiya reluctantly gave him some tips on how to spin his chakra, after which Naruto proclaimed that he would finish this first step and master the Rasengan in three days. Jiraiya informed him that the Fourth Hokage, the Rasengan's creator, created the Rasengan after three years' hard work. While thinking, Naruto sees a cat playing with the water balloon. When the cat pops the balloon after batting it around, Naruto gets an idea and finally manages to break the balloon himself.