Mostly revolving around interactions with the lwa, Vodou ceremonies make use of song, drumming, dance, prayer, possession, and animal sacrifice. Practitioners gather together for "sèvices" (services) in which they commune with the lwa. Ceremonies for a particular lwa often coincide with the feast day of the Roman Catholic saint that that lwa is associated with. The mastery of ritual forms is considered imperative in Vodou. The purpose of ritual is to "echofe" (heat things up), thus bringing about change whether that be to remove barriers or to facilitate healing.