Hex (1980)

Constantly mistreated by her cruel husband, the frail Chan Sau-ying awaits certain death from tuberculosis. The new servant girl, Kei-wah takes pity on her mistress' plight and the pair proceed to drown him one evening. They dump his body in a near-by pond but Sau-ying believes that the man's bloated corpse has risen from the bog to seek vengeance.