Gravity Theater: Psychological Metaphor of Mass Perception The difference in physical mass between the 27kg fat sex doll and the 52kg full body sex doll hides psychological metaphors. The former satisfies the secret desire for "overwhelming existence" through a heavy sense of existence; the latter caters to the fetish psychology dominated by the desire for control with a light composite skeleton. The difference in muscle load when users carry it inadvertently becomes a biofeedback instrument for the intensity of desire - those who are willing to purchase hydraulic brackets to move fat sex dolls are actually paying for their own persistence.