Who are these people?

I was watching The Countdown Reflection, then I noticednthem

I think that either Raj or Howard could have been shown as a Mathematician instead of their original profession. What do you think if any one of them being a mathematician would have made the show better or worse?

I want to watch this episode ASAP but don't know which it is;

One scene (I think at the end) where the duration of the episode was the four guys (or maybe two of them actually) are scared of some guy who hunted them down. The last scene two of them (or maybe all?) are behind the counter in 4A with the lights out as the guy bangs on the door.

Maybe early-mid series.

Bernadette tells the story that her company had come up with some drug that was supposed to do some particular thing, but had a horrible side effect, so they repackaged it as something else... anyone remember which episode that was? Thanks