An aspergillum is the implement, distinct from the vessel that holds the water, used to sprinkle holy water during Christian rites of blessing. Its most common form is a metal rod terminating in a perforated hollow ball, sometimes ornately worked in silver, which is dipped into a bucket-shaped vessel called an aspersorium or holy water stoup and then shaken or flicked toward the person, object or space being blessed, the perforations scattering the water in a fine spray rather than a single stream. An older and still-used alternative is a bundle of natural bristles, or, drawing on the biblical precedent of hyssop branches used for ritual purification in the Hebrew Bible, an actual branch, tied and dipped directly into the water.
In the Roman Catholic Mass, the aspergillum is used in the optional rite of asperges, most commonly on Sundays, in which the priest sprinkles the congregation with holy water while a chant recalling baptismal cleansing is sung, before the penitential act or in its place. It appears more broadly across Catholic and Orthodox practice in the blessing of homes, vehicles, religious objects, graves and, in some traditions, agricultural fields and animals, any occasion calling for holy water to be applied to multiple people or a wide area rather than administered individually by hand.