On the DC3, the Pilots could tell when the flight attendant walked to the rear of the aircraft because the autopilot applied forward trim. This is an adjustment the pilot makes to enable the aircraft to fly level without having to apply forward or backward pressure on the controls.
At the beginning of a flight when the aircraft is heavy with fuel it will fly slow and nose up, as fuel burns off it gets lighter and flys faster, the nose then needs to be moved down or it will climb.