The Fake Smile

is episode 36 of the Naruto: Shippūden anime.

Synopsis
Team Kakashi heads out for the Tenchi Bridge. Sakura and Naruto come down hard at Sai for making fun of their former team-mate, Sasuke. Seeing the tension in the team, Yamato decides they need to improve on teamwork and uses the Wood Release technique to create a wooden cage, threatening to lock the trio up unless they behave. Sakura is shocked to see Yamato using the secret techniques that only the First Hokage was said to possess. Given an ultimatum between being locked up or spending the night at a hot springs by Yamato, the team chooses to visit the springs to improve team cohesion. Despite this fact, Naruto still despises Sai. To cheer himself up, Naruto decides to try peeping on the women bathing over the wall. However, Yamato shares the story about Tsunade beating Jiraiya like a drum, prompting Naruto to be paralyzed for a few hours in fear of Sakura doing the same thing to him.

Trivia

 * It appears that Naruto has taken after his Master Jiraiya's pervy habit of peeping on women bathing.