The kartika is one of the most prominent weapons used by Buddhism's wrathful deities, both male and female. Continuously brandished by them or simply carried in their hands, its purpose is to chop up disbelievers.
This curved flaying-knife is modeled on the Indian "knife of the butchers", used for skinning animal hides. The gibbous crescent of its blade, which terminates in a sharp point or curved hook, combines the flaying implements of a cutting-knife and scraping blade, and the piercing activity of a dagger or pulling-hook. The blade's crescent is used for cutting through flesh and scraping it clean, separating the outer and inner as "appearance and emptines". The sharp hook or point of the blade is used for the more delicate acts of flaying: the initial incising of the carcass, the pulling out of veins and tendons, and cutting around the orifices of the skin.
An interesting but somewhat disturbing legend is related about the Mahakala "protector chapel" at Samye monastery in Central Tibet.
Traditionally, this forbidding chapel was kept locked for most of the year and entry into its precinct was rarely permitted. The attendant monk who supervised the chapel would each year ceremoniously replace an iron chopper and wooden chopping board which had become blunt and worn down by its nocturnal activities.
Even though the chapel was locked and empty, at night the screams of the ethereal miscreants hacked under Mahakala's chopper could be clearly heard from outside the chapel.
In Mahakala's symbolism the curved knife cuts through the life veins of enemies such as oath-breakers and hindering spirits; and his skull cup is filled with the heart-blood of these enemies. This crescent shaped chopper, held by deities such as Mahakala, corresponds in shape to the cavity of the skull cup and functions to make "mincemeat" of the hearts, intestines, lungs, and life-veins of enemies hostile to the dharma, which are then collected in the skull cup. As mentioned, a similar crescent shaped hand cleaver is used in oriental cuisine to chop meat and dice vegetables.
Just as the thunderbolt is typically paired with the bell, so do the chopper and skull cup generally accompany each other. The symbolism of the two pairs may be the same. Since the chopper is the instrument for cutting through the fog of ignorance, it represents method, the masculine principle, while the cup symbolizes wisdom, the feminine principle. In many ways, the chopper serves the same purpose as the dorje or the phurpa and is employed in rituals of exorcism by priests and shamans.