Leonard is granted a trip to Geneva to see the CERN supercollider. Although Sheldon cites their Roommate Agreement , which requires Leonard to take him if ever invited to CERN, Leonard chooses to take Penny for a romantic Valentine’s getaway.

During his campaign, Sheldon hugs Penny after she briefly agrees to talk to Leonard. However, Penny catches the flu just before the trip. Leonard tries to take Sheldon instead, only to find that Sheldon has also caught the flu from the hug.

"The Big Bang Theory" The Large Hadron Collision (TV ... - IMDb

is the 15th episode of the third season of The Big Bang Theory , which originally aired on February 8, 2010. In this Valentine's Day-themed episode, Leonard is invited to visit the Large Hadron Collider in Switzerland and must choose between taking his girlfriend, Penny, or his roommate, Sheldon. Plot Summary

Leonard ultimately travels to Switzerland with Raj , who is thrilled to enjoy the romantic amenities—like champagne and chocolates—originally intended for Penny. Key Characters & Cast