A tree grows next to a greenhouse enclosing an imitation of the tree. The imitation greenhouse tree wants to be big and impressive like the tree outside, so it does its very best imitation of a real tree.
The greenhouse tree realizes that its imitation will never be as good as the real thing. When it realizes this, the tree moans (も) aloud. The tree is still kinda tiny, so the moan isn’t very loud, but it is still pretty strange to witness. Speaking of witnesses, Bobo (ぼ) the clown sees this greenhouse tree moaning and decides to take it for his next clown show. Surely this miniature moaning tree can be worked into Bobo's next clown act.