An individual who turns to the lwa to harm others is a "bòkò" or "bokor", and described as someone who "sert des deux mains" ("serves with both hands"), or is "travaillant des deux mains" ("working with both hands"). These practitioners deal in "baka", malevolent spirits sometimes contained in animal form. Bòko are also believed to work with "lwa acheté" ("bought lwa"), because the good lwa have rejected them as unworthy. Their rituals are often linked with Petwo rites, and are similar to Jamaican obeah. According to Haitian popular belief, these bòkò engage in "envoimorts" or "expeditions", setting the dead against an individual to cause the latter's the sudden illness and death.