We did the same thing on the WC-135. New right-seater, plane on autopilot over the Pacific at FL 35.0, several hours of basically nothing until we arrive at Yokota, Misawa, or Kadena.
The left-seater checks off and says he's going aft to get coffee, leaving the new guy watching the gauges, monitoring radios, and reading the newspaper. But he's not getting coffee - he's passing the word around that everybody should slowly, one at a time, head for the aft galley and stay there until given the signal.
The signal cues everybody to rush forward to the flight deck, all at once.
The autopilot pitch axis senses an abrupt nose-down change in the aircraft's attitude, and immediately goes into an emergency climb while sounding alarm horns. The yoke comes back smartly into the right-seater's lap, and if he was reading the newspaper, oh well...