|A juvenile Burmese Python constricting a rat.|
The study found both species constrict prey vigorously using coils of 1–4 loops. Reticulated Pythons exerted maximum pressures of 8.27–53.77 kPa, with larger individuals exerting significantly higher peak pressures than smaller individuals. Burmese Pythons constricted with maximum pressures of 18.0–42.93 kPa, with larger individuals also exerting significantly higher peak pressures than smaller individuals The species or the number of loops in a coil did not significantly affect peak
pressure in either species.
Constriction pressures exerted by both pythons scale differently from those of other snakes, many of the highest pressures were probably enough to force blood into the brain at high pressure in mammalian prey. In addition to suffocation, circulatory arrest and spinal dislocation, the authors propose the ‘red-out effect’ as a fourth possible mechanism of prey death by constriction. The redout effect describes the effect of negative gravity on jet pilots during extreme flight manoeuvres, in which vision becomes reddened by uncontrollable blood flow to the brain and eyes. When fighter pilots experience negative gravitational accelerations (G-forces), they incur a rush of blood to the brain that causes rapid loss of consciousness. Constriction pressures above the venous blood pressure of the prey will impede blood flow and oxygen delivery to tissues. Pressure from constriction dramatically higher than the prey’s blood pressure could force blood away from the site of constriction and into the extremities, including the head and brain. Blood being pushed into the brain during peak constriction could cause the same red-out effect described above for pilots, and could cause extensive ruptures in cranial blood vessels.
Penning, D. A., Dartez, S. F., & Moon, B. R. (2015). The big squeeze: scaling of constriction pressure in two of the world's largest snakes, Python reticulatus and Python molurus bivittatus. Journal of Experimental Biology,218(21), 3364-3367.