A kut is a long event. It runs in numbered sections, each addressed to a different god or group of the dead, and the practitioner changes costume between them so that the room can see which presence is being dealt with. The bells work across the joins. Shaken in the hand, in fast repeated bursts, they open a section, hold the rhythm against the drums and gongs of the accompanying musicians, and mark the point at which the practitioner begins to speak in the voice of the spirit rather than her own. Clients and family present at the rite respond to that shift, because what is said in that voice is the part they came for: a judgement on a household problem, a message from a dead relative, a demand for something to be put right.
The bells are the practitioner's own equipment. Along with the fan, the knives and the costumes, they are acquired at or after initiation, or inherited within a line of practice, and they are kept with the practitioner rather than at the house where a rite is held. That matters for how the object should be described. A particular set of bells is tied to a particular person's practice and to the gods she serves, and treating one person's regalia as a general specification for Korean shamanic equipment misrepresents a tradition in which the personal relationship is the organising fact.