"If two people share one, their destinies become intertwined. They'll remain a part of each other's lives no matter what. C'mon, I know you want to try it." ~ Riku
Later on, Sora goes to the Secret Place. He sees a carving of himself and Kairi that the two of them made when they were younger. Sora--after having learnt the signifigance of a paopu, but being too shy to actually share one with Kairi--picks up a stone and carves a picture of him giving a paopu to Kairi. Later on, after you close the door to Kingdom Hearts, and Sora and Kairi get separated between worlds, Kairi goes back to the Secret place. She sees Sora's additiong to the carving and in tears of both happiness and sadness, Kairi picks up a rock and mimics the action.