The Big Bang Theory Season 2 Episode 16 “The Cushion Saturation”
After a paintball game, Penny and Sheldon are at it again with their feud (Penny accidentally shot Sheldon’s couch cushion and had it dry-cleaned), and Wolowitz and Leslie find common ground and romance. The dry cleaning takes a week and Sheldon withdraws during that period.
Meanwhile, Leslie and Howard start sleeping together at Howard’s home, and it turns out that Leslie is in control of the relationship; he needs Leslie to fund a work project, and she gets what she wants by threatening to take away a trip to the CERN Large Hadron Collider project in Geneva. After the initial reluctance, Howard begins to accept that he is just “arm candy”.