FYI, The version of the story I always heard had the snake attacking with its fangs, not with its tail, although I suppose there could be multiple breeds of hoop snakes that behave in different ways, or just snakes that are adaptable and can use either of various strategies as is convenient.
Anyway, there are at least three axes of symmetry to be considered:
- Head first vs. tail first.
- Conventional strike (strike with body in normal position) or inverted strike (body is upside down when striking)
- Rolling straight (like a hula hoop) or half-twist (twisting part of the snake's body around a half turn as it rolls, so that the top of the snake is on the outside of one part of the loop while the bottom of the snake is on the outside of another part).
For instance, it seems to me that the "head-first conventional straight" (HFCS) hoop snake is at its most dangerous when it sits around lying on its back (or flips to assume that position), when its tail pointed towards you, and its head raised and partially folded over its body, but its upper body pulled back a bit, tense, ready to strike. (A normal snake (e.g. a cobra) ready to strike would be in a similar position with its upper body, but with its lower body right-side up and pointed away from you, rather than toward you. A cobra strikes by pushing its upper body forwards with its lower body, while straightening and lengthening the upper body. A hoop snake would strike by pulling its upper body forwards with its lower body, while straightening and lengthening its upper body.)
From this position, if you are nearby, a HFCS hoop snake can strike directly at you, over its upside-down lower body. If you are some distance away, it can strike over itself, lifting its tail for its mouth to grab it, then roll forwards one or several times (accelerating as it goes) until it gets into striking distance, at which point it lets go of its tail as it reaches the top of the loop and then launches itself even higher into the air with the tip of its tail as it leaps to strike.
A HFCS hoopsnake might easily get into this position by appearing to run away from you, then roll over and strike. It might even pretend to be "prey" to predators, luring them into chasing it and hence getting close before suddenly rolling and counterattacking.
The "head-first inverted straight" (HFIS) variety strikes in a similar fashion, but the snake doesn't roll over before striking, and therefore rolls with its eyes on the inside of the loop and eventually strikes with its head upside down. Having its eyes on the inside of the loop would obstruct its vision a bit (having to look around its own tail), but these snakes would have the advantage that the side of its body that is best armored for gliding along the ground is on the outside of the loop, and it is not having to roll on its back.
The "tail-first inverted straight" (TFIS) variety would start facing you on the ground (like a normal snake), and then "strike" its tail over itself, grabbing the tail in its mouth, rolling to accelerate, and then letting go at the front of the loop (when it can see you) to jab with the tail. This version seems a bit less dangerous to me, since the times that the snake can see you to know where it is going are those when its head is on the ground (rather than in the air) with limited visibility, and right before the time when it lets go of its tail, it is actually facing away from you.
And an "tail first conventional straight" (TFCS) variety would roll over facing you so it is upside down, strike its tail over itself, do the tail grab, roll, push off with the top of its head, and strike with the tail upside down. This seems the least dangerous of the four, since it would be pushing its eyes into the dirt as it strikes, which would make for poor targeting.
Most feared of all, however would be the half-twist snakes (headfirst and tailfirst varieties) which continually twist their bodies a half turn around as they roll horizontally, so that their ground-facing scales are on the ground at the bottom of the loop, but their heads are also looking over the top of the loop at you, with unobstructed vision.
A variation of the half-twist snakes, the Moebius snakes (which give the tail a half twist before grabbing it) would probably mostly end up getting really confused before being able to roll very far, as they would be alternately striking with the top and bottom of their heads against the ground as they rolled. The bizarre, oddly hypnotizing spectacle of a Moebius snake on the roll could, however, stop potential prey in its tracks from sheer amazement and confusion long enough for the snake to strike.
