Trivia: Creator Dan Harmon was fired during season four and rehired for season five. Harmon attracted some controversy when he finally watched season four and made several vulgar jokes about it, as he felt it was like an "unflattering impression." He later apologized and stated that he had a lot of respect for the writers and season four showrunners for trying their hardest to replicate his work and keep the show alive, and said he thought many of the jokes and the Rachel character were great.
Advanced Documentary Filmmaking - S4-E6
Trivia: When Chang and Jeff are discussing his Changnesia, Chang says his short-term memory is getting better and rolls up his sleeve to read the words "side-effect" that he's written on the inside of his arm. On the side of his arm that's facing the camera, he's written a reminder to "Rent Memento." (00:08:50)
Cooperative Escapism in Familial Relations - S4-E5
Trivia: During the fifth episode of Season Four ("Cooperative Escapism in Familial Relations"), Dean Pelton is shown to be wearing a cowboy's outfit during one scene. This is a very close replica of the cowboy costume Jeff Winger wears in the Season One Halloween episode "Introduction to Statistics." Later, during the seventh episode of Season Four ("Economics of Marine Biology"), when Pelton's pants are pulled down, it becomes clear that he is wearing the same underpants as Jeff from the Season One episode "Physical Education." It is confirmed in the DVD commentary that these are just two of many subtle examples of Pelton emulating Jeff's style, due to Pelton's obsessive crush on Jeff.
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