橡树

橡 = 木 + 象 : Marie Curie (xi) wants to plant some oaks (橡) in the anglepod's bathroom (ang4), so she had the KFNB Elephant (象) transport young oaks to the bathroom. In exchange she provides the train with a lot of Christmas trees (木) to be used as fuel for the steam engine.

树 = 对 + 木 : Sheldon Shrimp cultivates a Christmas tree in the space station's bathroom. He is very happy that he found the right tree, just the one he imagined, and—in his mind—marks of the tree he imagined with a big green check mark.