Complex sentence: Not knowing what Sasuke and Naruto are whining about, Kakashi sits down just as the poisoned dart is launched at him, nearly hitting him but instead hits a frog, who then dies of laughter.
Split into simpler sentences: Not knowing what Sasuke and Naruto are whining about, Kakashi sits down just as the poisoned dart is launched at him, nearly hitting him. Instead, it hits a frog, who then dies of laughter.