In Eucharistic Prayer III, the Vere Sanctus (Father, you are holy indeed) is spoken by the principal celebrant alone, with hands extended.
From the Supplices ergo te, Domine (And so, Father, we bring you these gifts) to the Respice, quaesumus (Look with favor) inclusive, all the concelebrants speak all the following together: The Supplices ergo te, Domine (And so, Father, we bring you these gifts) with hands extended toward the offerings; The Ipse enim in qua nocte tradebatur (On the night he was betrayed) and the Simili modo (When supper was ended) with hands joined; While speaking the words of the Lord, each extends his right hand toward the bread and toward the chalice, if this seems appropriate; as the host and the chalice are shown, however, they look at them and, afterwards, bow profoundly; The Memores igitur (Father, calling to mind) and the Respice, quaesumus (Look with favor) with hands outstretched.
The intercessions Ipse nos (May he make us an everlasting gift), Haec hostia nostrae reconciliationis (Lord, may this sacrifice), and Fratres nostros (Welcome into your kingdom) are appropriately assigned to one or other of the concelebrants, who speaks them aloud alone, with hands extended.