Fifield found rolled up

leading from

Fifield Monster

Mutant Fifield with legs wrapped over his shoulders (Cinefex #130, p49)

When Fifield in his transformed state returns to the Prometheus, he is found with his legs hideously bent over over his shoulders. My initial thought was that this was a play with the idea of what the organic box Alien scene that Dan O'Bannon mentioned had been filmed and cut out, but Walter Simonson had seen it in a rough cut and so included it in Alien: The Illustrated story. Ridley's original storyboard simply states that he is crouching and had the idea of the character possibly being in a pit and dressed in other body parts. With his lower body in a put, they draped dummy legs over his shoulders.

Ridley's Storyboard

In Ridley's earlier film project Tristan and Iseult, a post-apocalyptic retelling of tradational celtic legend, in one of his storyboards he included something that became labeled as a Froudian, loosely inspired by something he had seen in the art of Brian Froud, an illustrator much renowned for his illustrations of faeries and goblins, but this strange almost thing has its legs oddly drawn with the shoulder behind the knee,  arm coming out from below the upper bent leg with the arm and then the elbow outside of the lower leg. 

"Froudian" (detail from image below)

A nitsilic priest and a "Froudian" creature amidst the floating rocks in Tristan And Iseult

It is a little bit different from what is happening to Fifield, his whole body appears to be bent backwards below ground level in a way that isn't human, and the upper legs are bent backwards as well. So what Walter Simonson saw in the alien folded up into an organic box seat appears to have the same sort of impact to tell us that there's something not quite humanoid about the body of this vaguely humanoid (See organic box like thing)

"organic box-like thing " from Alien the Illustrated Story