"Infiltration: The Den of the Snake!" (潜入!毒蛇の巣窟, Sennyū! Dokuhebi no Ajito) is episode 47 of the Naruto: Shippūden anime.
After recovering from Sasuke's genjutsu, Sai gives Orochimaru an envelope containing information from Danzō about Konoha's Anbu. Arriving near Orochimaru's hideout, Yamato gives Sakura and Naruto wooden seeds which are imbued with his chakra and would enable him to track them down if they get lost. Yamato reveals that he was able to track Sai with the same seeds, which he secretly put in Sai's food. In the hideout, Kabuto locks Sai in a room, and the latter summons a bingo book. Outside, Yamato is able to open a tunnel into Orochimaru's hideout, and he, Naruto and Sakura manage to travel to Sai's room undetected.