In the same manner he addressed the Pratihartri; 'Pratihartri, if you, without knowing the deity which belongs to the pratihâra (the hymns of the Pratihartri), are going to sing it, your head will fall off.' They stopped, and sat down in silence.

In plain words: He gives the same warning to the Pratihartri, the priest who sings the responding part. All three priests stop and sit in silence.