उपमन्त्रयते स हिंकारो ज्ञपयते स प्रस्तावः स्त्रिया सह शेते स उद्गीथः प्रति स्त्रीं सह शेते स प्रतिहारः कालं गच्छति तन्निधनं पारं गच्छति तन्निधनमेतद्वामदेव्यं मिथुने प्रोतम् ॥ २.१३.१ ॥
In plain words
He invites her: that is the hiṃkāra. He makes his proposal: that is the prastāva. He lies down with the woman: that is the udgītha. He lies facing the woman: that is the pratihāra. He comes to the moment: that is the nidhana. He comes to the end: that is the nidhana. This is the Vāmadevya chant woven upon coupling.
The commentators
Chāndogyopaniṣadbhāṣyam· bhāṣya
उपमन्त्रयते सकेत करोति, प्राथम्यात् स हिंकार । ज्ञप यते तोषयति, स प्रस्ताव । सहशयनम् एकपर्यङ्कगमनम्, स उद्गीथ , श्रेष्ठ्यात् । प्रति स्त्रीं शयन स्त्रिया अभिमुखीभाव , स प्रतिहार । काल गच्छति मैथुनेन, पार समाप्तिं गच्छति तन्निधनम्, एतद्वामदेव्य मिथुने प्रोतम्, वाग्वम्बुमिथुनस- बन्धात् ॥
In plain words
The preliminary address with a sign is the hiṃkāra, because it comes first. The communication of desire and the giving of satisfaction is the prastāva. Lying together on a single bed is the udgītha, due to its pre-eminence. The woman turning to face her partner as they recline is the pratihāra. Time passing through intercourse and reaching its complete end is the nidhana. Thus the Vāmadevya chant is woven into sexual union, based on the underlying correspondence of speech and water.
Close to the Sanskrit
Addressing lovingly makes a sign, from priority that is the hiṃkāra. Makes known, satisfies, that is the prastāva. Lying together, going to a single couch, that is the udgītha, from pre-eminence. Towards the woman lying, the turning to face each other, that is the pratihāra. Time goes with sexual union, the completion goes to the end, that is the nidhana. This Vāmadevya is woven in the union, because of the connection of the speech-water pair.