Cattle trucking sign

While having a quick reading of an old book; Questions and Answers in Medicine for Students by B.T Cooper and M.J Hall(1984), my attention was caught by a term of cattle trucking when the author describes the sign of death along side with absence of respiration, absence of pulse or heart beat and fixed dilated pupils. I wonder how do they derive this name? This sign can also been found in central retinal artery occlusion.. it simply means segmentation of the blood column in the arteries

image source: patient.co.uk [link]