This is often called the Fraction Rite. While the Agnus Dei is chanted, the priest breaks the Host in two and then breaks off a particle and drops it into the Precious Blood. While doing this, he says quietly “May this mingling of the Body and Blood of Our Lord Jesus Christ bring eternal life to us who receive It.”
DISCLAIMER: Catholic Answers has turned over the archive to Catholic-Questions.org and no longer owns, manages, or moderates the forums. For additional apologetics resources please visit www.catholic.com.