Shhh! is the 20th episode of Season 5 and the 124th of Adventure Time. It aired May 13, 2013.
Finn and Jake decide to play a game of "who speaks first", using signs as their only means of communication, wagering that whoever talks first will be "really disappointed." They eat breakfast in the kitchen, where they encounter BMO, who plays his favorite song to them. BMO is startled when they do not speak, and thinks they are not the real Finn and Jake, so he hides in a hole in the wall, continuing to play his favorite song to calm himself down. Finn and Jake then try to communicate with BMO in many ways (with Jake entering the hole in the wall and finding various creatures there), but all without success.
Meanwhile, BMO had invited a group of Bikini Babes over to dance, and the Bikini Babes begin to cluster at the door of the Tree Fort. The Bikini Babes fly on top of the house, where they hear BMO playing his favorite song. Finn and Jake try one last time to reach BMO by using axes to chop down their kitchen wall, but they end up creating a rift in the wall that extends to the ceiling, opening it up, so the Bikini Babes fall inside. BMO appears and yells at them to attack Finn and Jake. While the Bikini Babes weakly beat up Finn and Jake, Jake cries uncle, signaling that he has lost the game. BMO then realizes that Finn and Jake were their real selves all along. The two try to explain what happened, but BMO cuts them off to say that he doesn't care and invite them to party. Finn, Jake, BMO and the Bikini Babes start dancing, and the Party God crash-lands through their roof to join in.
This episode was dedicated to Armen Mirzaian, former storyboard artist of Adventure Time. He died in Febuary of 2013 in a car accident.