Laughing Shino

is episode 186 of the original Naruto anime.

Synopsis
Naruto and Shino are sent on a mission to Motoyoshi Village to help a man inherit his wealth before his greedy siblings by standing in at the funeral in so the man won't be tempted to laugh and lose his inheritance. On the way they encounter an old woman who is leaving town who gives them a suspicious warning. While guarding the man and trying to prevent him from laughing, Shino eats dinner first to prevent any poison from entering their host because his insects will neutralize the poison. He ends up laughing, and the insects won't neutralize the poison.