Foosball and Nocturnal Vigilantism - S3-E9
Character mistake: In the bonus clip where we see Leonard's online video about frozen food, the first thing he says is, "This is November 29th". However, if you look under the video, you can see the video was uploaded on Nov 26, 2011, which is three days earlier.
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