What had Tree-ear secretly done to one of Min's pots?

Tree-ear, always impressed with Min's work, worked hard to replicate it. Every evening he worked a piece of clay he brough home with him, until finally he produced one petal he believed was as beautiful as Min's. Finally, he took the petal and substituted it for one Min had drying on his shelf. Min didn't know it, but the pot was displayed for the emissary..... Tree-ear was proud that his substitution hadn't been detected but ashamed of the act itself.