Surprise Attack! Naruto's Secret Weapon!

is episode 45 of the original Naruto anime.

Synopsis
Using Kiba's own smokescreen as a cover, Naruto disguises himself as a third Kiba through use of the Transformation Technique and tricks Kiba into knocking Akamaru out, which only serves to anger Kiba. Naruto, however, is still at a disadvantage due to Kiba's pill-enhanced chakra and superior speed. Furthermore, Orochimaru's seal disrupts his already low chakra reserves, hindering Naruto's ability to build up enough chakra for his new technique. Kiba's onslaught ends when Naruto accidentally farts in Kiba's face due to straining himself too hard, resulting in a disastrous effect on him due to his enhanced sense of smell. Naruto then finishes the battle with Naruto Uzumaki Combo, a technique he based off of Sasuke's winning move that utilises his shadow clones.