Having identified folk artifacts, the professional folklorist strives to understand the "significance" of these beliefs, customs, and objects for the group, since these cultural units would not be passed along unless they had some continued relevance within the group. That meaning can however shift and morph, for example: the Halloween celebration of the 21st century is not the All Hallows' Eve of the Middle Ages, and even gives rise to its own set of urban legends independent of the historical celebration; the cleansing rituals of Orthodox Judaism were originally good public health in a land with little water, but now these customs signify for some people identification as an Orthodox Jew. By comparison, a common action such as tooth brushing, which is also transmitted within a group, remains a practical hygiene and health issue and does not rise to the level of a group-defining tradition. Tradition is initially remembered behavior; once it loses its practical purpose, there is no reason for further transmission unless it has been imbued with meaning beyond the initial practicality of the action. This meaning is at the core of folkloristics, the study of folklore.