I also agree with this theory ... The way I look at it the lower to the ground the prey item is the more likely the snake is to be less intimidated by it .... For instance a med rat on all four legs is maybe 3 inches tall, to where if the rat is doing a headstand it is somewhere around 6 to 7 inches tall (more intimidating to some snakes) .... This is not always the case as some are more timid than others .. I have some snakes that I can barely get the f/t in the tub before the snake snatches it ... Just a way I look at it, every snake is different