The First Chang Dynasty - S3-E21
Continuity mistake: Troy and Britta are spying on the school behind a hedge through binoculars. When Annie pops up, Troy sets them down. As the camera cuts between Britta and Annie to Troy, the binoculars disappear and reappear.
Answer: It was part of the plot that when the boiled yam was dropped it looked like it was stepped on (which it never was). So there was no way to tell the difference between the flesh being soft because it was boiled or because it was stepped on (in the show that is, I don't know if one could tell the difference in real life). Plus, the rest of the yam wasn't boiled, so there was no evidence the yam was sitting in boiling water.
Bishop73