The staircase implementation

This episode of “The Big Bang Theory” talks about how Leonard tells to Penny why he didn’t go out of the apartment for all the argue that he had with Sheldon about everything, the thermostat and the degrees, seeing or no Babylon 5.
He tells how he met Sheldon and how Sheldon ruins things like a meeting with a girl, but Leonard tells too that Sheldon saves him to tell Joyce Kim (the girl) about his governmental research, because she was a North Korean Spy. Leonard tells to Penny how Sheldon saves him from an explosion of combustible gel and how its
The episode is very good, and like all the “The Big Bang Theory” episodes has a lot of jokes and humor. The good part of the episode is that there we know about Leonard; Sheldon; Raj and Howard past how all of them met, and how the elevator explode. And how all of them have to up and down three flights of stairs in the day.

The group in the beginning, like it appears in the "Flashback" of Leonard
when he tells the story to Penny.