Survivor Season 21 Episode 4 (Survivor s21e04) with title “Pulling the Trigger” aired on Wednesday, October 6th 2010 at 08:00 pm via CBS Network.
Here is summary for Survivor Season 21 Episode 4 :

NaOnka and Kelly B. exchange a war of words over the hunt for the hidden immunity idol, and a secret is revealed that solidifies a powerful alliance. At tribal council, another castaway is voted out of the game.