Valmiki Ramayana Yuddha Kanda Sarga 100 Shloka 39
Original Shlokaतेभित्त्वाबाणरूपाणिपञ्चशीर्षाइवोरगाः ।।6.100.39।। श्वसन्तोविविशुर्भूमिंरावणप्रतिकूलिताः ।
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ते they, पञ्चशीर्षाः five headed, उरगाःइव like serpents, बाणरूपाणि in the form of shafts, भित्त्वा penetrated, रावणप्रतिकूलिताः when repelled by Ravana, श्वसन्तः hissing, भूमिम् earth, विविशुः entered
The five headed serpent like arrows released by Rama penetrated and having been repelled by Ravana they entered the earth hissing.