Continuity mistake: Katniss, Coin and Heavensbee are discussing Katniss staying in 13 and shooting some propo's to show she is still alive. Heavensbee has a pen in his hand that has the cap off. Camera cuts to Katniss and then back to Heavensbee and the pen lid is now replaced. In the shot of Katniss we see his arms and they do not make the motions of replacing the cap.
Picture added by A Demon