The Trigger of Rage!! (怒りの引き金!!, Ikari no Hikigane!!) is chapter 291 of the Naruto manga.
Naruto demands that Orochimaru give Sasuke back. Orochimaru tells him to try using force. Naruto promptly manifests a one-tailed chakra shroud and attacks him, sending him back into the forest. Seeing this, Yamato remembers a conversation he had back in Konoha about Naruto's tailed-transformations. Naruto enters tailed transformations as he loses his temper, becoming more dangerous to himself and others with each new tail. Since the Nine-Tailed Demon Fox would be released if he reached nine tails, Yamato is to prevent this from happening. Orochimaru remarks on this when he returns, noting that Konoha should be grateful for giving Yamato Wood Release abilities. He voices his interest in examining Yamato and seeing how Naruto compares to "his" Sasuke. Naruto grows infuriated by the reference to Sasuke as property and reaches three tails.