After all of them were disturbed by Sheldon's annoying behavior, they got together to discuss how to solve this problem.

Suddenly Raj said what if something were to happen to Dennis Kim so he was no longer a threat to Sheldon, then Sheldon would be back to his normal life, and their problem would be solved.

Leonard thought what Raj's talking was about murdering Dennis Kim, and surprisingly he wasn't totally in the state of denying this suggestion.

casual: in the state of relax whether your are or pretend to be.

link: relationship between two things, or one thing is the cause of another.

curious: interested in something and you want to know more about it.

design: if you want to design a machine or building, you make a plan and drawings very detailed from which it can be made of

threat: something that is unpleasant and might happen to someone.