The rollers (the narrow white tubes) reverse the direction in which the rear wheels push on the ground. Imagine a pair of two gears meshed together or rubber wheels. If one gear turns clockwise, the other must turn counterclockwise. The truck's rear wheels are like the driving gear in this case, and the rollers act like the other gear. The tire turns "clockwise", and the roller "counterclockwise", just like putting the vehicle in reverse (the front wheels can spin freely in either direction). The chains serve as axles for the rollers, keeping them in place under the wheels. Makes sense?
They also used headrests at some point simply because the exposure times were really long, and people tend to make micro-movements with their heads involuntarily. So the fact that you can see some sort of support (like in the last picture) is by no means definite proof that you're looking at a dead person. At least not at the time the photo was taken.
Were those really the emotions the various models were feeling when they were photographed or is this just a test to try to guess the puzzlemaker's opinion of the models' emotions? Pesky humans.
It would be a real-life video game challenge.
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Size m suggested colour
Pesky humans.