Question: Why does Fr. Hardesty bow his head at different parts during the Mass? Does he have a crick in his neck?
Answer: Yes! Also (!) it is because of a long-standing tradition in Catholic worship to bow our heads out of honor and reverence. This is not only for the priest, but for the people too. This was a very common practice in the older form of the Mass and in fact is still in the instructions today, for the new form of the Mass. In the Extraordinary Form there are many different types of bows of the head and body for many different occasions in the Mass. These have been simplified in the Ordinary Form but are still there.
GIRM 275 says: “A bow signifies reverence and honor shown to the persons themselves or to the signs that represent them. There are two kinds of bow: a bow of the head and a bow of the body. A bow of the head is made when the three Divine Persons are named together and at the names of Jesus, of the Blessed Virgin Mary, and of the Saint in whose honor Mass is being celebrated.”
According to the traditional practice, the head bow in worship is made by solemnly drawing the chin to the chest rather than the nod that you see guys give each other on the street. Some bow the head when they hear “Jesus” others just when they hear “Jesus Christ” (as is my practice). During the homily, rubricians back in the day advised that you only needed to bow the head (or doff the biretta) at the first mention of the name of Jesus – otherwise you could be bowing your head quite a lot! In the Extraordinary Form, this is indeed quite comical when a preacher in a flurry of piety repeats the name of Jesus every other sentence and you see birettas at the sedillia and choir jumping up and down!