Sumantra’s head and sense of speech also became successful. That is stated in this verse.

His head became successful when he offered his obeisances unto the Lord with humility, that is, by offering obeisances with the eight parts of his body. Sumantra’s sense of speech became successful as a bard [glorifying the Lord].

NOTE. Regarding the perfection of the head and the sense of speech, the Mukunda-mālā-stotra (46) notes:

praṇāmam īśasya śiraḥ-phalaṁ vidus
tad-arcanaṁ prāṇa-phalaṁ divaukasaḥ
manaḥ-phalaṁ tad-guṇa-tattva-cintanaṁ
vacaḥ-phalaṁ tad-guṇa-kīrtanaṁ budhāḥ

“The wise inhabitants of the heavenly regions know that the perfection of the head is to offer prostrate obeisances to the Supreme Lord, the perfection of the life-breath is to worship the Lord, the perfection of the mind is to ponder the details of His transcendental qualities, and the perfection of speech is to chant the glories of His qualities.”

Pañcarātra-pradīpa describes offering obeisances with the eight parts of the body as follows:

The Hari-bhakti-vilāsa tells how to offer daṇḍavat-praṇāma: Offer obeisances with eight aṅgas—your feet, knees, chest, hands, head, sight, mind, and words. With your two feet, knees, chest, hands and head touching the ground, and with your eyes downcast and half open, recite a suitable prayer while meditating that your head is under the Lord’s lotus feet.