To clarify - the red cabling and what its attached to is dynamic pressure measurement. The barrels are just to simulate passenger weight.

Nose section of the 747-8I prototype cabin.

The prominent black tanks store water which is shifted longitudinally (through the gray plumbing) in the aircraft during test flights. This allows precise control of the center of gravity position and measurement of the corresponding stability and control margins.

Also visible are the flight test pressure probe equipment, cabled with red wires and connected to dynamic pressure probes on the outside of the fuselage through specifically-replaced window panes (the right probes were disconnected at the time of the photo).