Although Robinson had fully prepared before firing the gun, the tremendous recoil generated by the gun not only made his body shake but also caused the strengthened pickup truck to unexpectedly rear up.
It should be noted that due to the dangers of the wilderness, this pickup truck had been reinforced and modified to enhance its defensive capabilities, greatly increasing the weight of the vehicle.
Even so, when Robinson, standing in the bed of the pickup truck, fired the gun, the strong recoil force resulted in him stabilizing his balance by directing the recoil force downward.
It was precisely because of this that the intense inertia forced down the bed of the truck, making the front of the pickup rear up.