Other mistake: Since Annie had completed the terrarium the group should have at least received a passing grade since the Professor made them a group of 7.
Introduction to Finality - S3-E22
Other mistake: During Leonard's "Let's Potato Chips" YouTube video during the ending credits, you can see the video reaches the end of the load/play bar (watch the circle), yet the video continues for several seconds. Once the circle reaches the end of the load/play bar, the video is over and won't continue.
Lawnmower Maintenance & Postnatal Care - S6-E2
Other mistake: Britta hits Abed in the face with a pillow, swinging in from the right, but when it connects, his face swings the other way, the same direction from which the pillow came. (00:16:50)
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