Oobi and Kako make a new friend in the park who seems different from them. Grampu explains that the girl is deaf, and helps Oobi and Kako learn some sign language so they can communicate with her. — NickJr.com (source)
Oobi, Kako, and Grampu are at the park. Kako holds up a cup-ball toy and tells the viewers about it. He and Oobi walk to the far side of the park to play with it. They try to play for a while, but they find it really hard to get the ball into the cup. A little girl appears and shows them how to play. The girl doesn't talk at all and leaves shortly after. The boys are impressed by her skills and tell Grampu about her, calling her the "cup-ball queen." Grampu asks for her name, but the boys realize they never heard it.
Kako spots the girl sitting on a bench with her mom. Grampu notices that she's using sign language and explains to the boys that she is deaf. Oobi and Kako are amazed, and they decide that they want to learn sign language so they can communicate with their new friend. Grampu, who knows a few movements in sign language, teaches them how to wave "hello." The boys use this symbol to greet the girl. The girl signs the letters for "Amy," and her mom tells the boys that it's her name. Amy's mom shows Oobi and Kako how to sign their own names. They also learn the signs for "friend" and "play." Later, Amy joins the boys in a game of tag.
The next scene is an interview segment where Uma talks with a boy and his deaf mother. She learns the signs for "fish" and "yellow." The scene cuts back to Oobi, Kako, and Amy at the park. Grampu tells the boys that they'll need to go home soon. Amy shows them the sign for "goodbye." Oobi, Kako, and Amy sign "goodbye" to the viewers as the episode ends.