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.
Sai was temporarily trapped in a powerful genjutsu from Sasuke's Sharingan, which frightened him. After recovering, Sai gave Orochimaru an envelope containing information from Danzō about Konoha's ANBU. On coming near to Orochimaru's hideout, Yamato gave Sakura and Naruto wooden seeds to ingest, which were imbued with his chakra and would enable him to track them down if they got lost. He revealed that he had been able to track Sai with the same seeds, which he had secretly put in Sai's food. In the hideout, Kabuto locked Sai in a room, and the latter summoned a bingo book. Outside, Yamato used a Wood Release technique to open a tunnel into Orochimaru's hideout, and he, Naruto and Sakura managed to travel to Sai's room undetected.