Mystery of Pain

is episode 160 of the Naruto Shippūden anime.

Synopsis
Konoha continues to fight off Pain while attempting to learn his secret. The Animal Path attacks the ANBU Interrogation Corps, and the Konoha ninja present must fight off a variety of different summons. Ibiki captures Animal Path in a Summoning: Torture Chamber, and tries to extract information about the enemy but to no success. Instead, torture is turned against him as Animal Path uses Ibiki's chest as a conduit for summoning the Giant Drill-Beaked Bird. In the end, Animal Path unleashes all of the Summons, which led to more trouble for the Konoha shinobi to handle. Meanwhile, Naruto finishes his Sage Mode training and attempts to bond with Fukasaku, so that he can move in Sage Mode, while the Toad Sage gathers Nature Energy. However, Fukasaku is rebuffed by the Nine-Tailed Fox, forcing the duo to find an alternate method for Naruto to enter Sage Mode in battle.