Cleaning up after an internet experiment Leonard discovers a letter in the trash can. He and Sheldon had been invited to present some research they had done together at a physics conference. However Sheldon does not believe in such things and says if he won't go no one can. Leonard defies him and says he will go and present the findings on his own. This causes a rift between the two which Penny tries to mend but accidentally makes worse. At the conference Sheldon appears and has a physical altercation with Leonard. In the end, the fight is captured by Wolowitz and put on Youtube.