He as found that there are five theories for its causation: 1) the labyrinthine (the ear contains two tiny sacs, the utricle and the saccule, and three semicircular canals .
But it is the utricle that responds to acceleration, and the saccule to deceleration.
When an animalcule touches the bladder (utricle) a flap snaps upwards; the beastie slips into the pouch; the trap springs shut.