When we approach the Precious Body to receive, we bow. Then we walk over to where another EM is holding the Precious Blood. Ought one to bow again before receiving the Blood? Ought one pause and bow as one passes if not intending to receive?
Yes, someone who chooses to receive from the chalice should bow before receiving, as the General Instruction of the Roman Missal states:
160 …When receiving Holy Communion, the communicant bows his or her head before the Sacrament as a gesture of reverence and receives the Body of the Lord from the minister. The consecrated host may be received either on the tongue or in the hand, at the discretion of each communicant. When Holy Communion is received under both kinds, the sign of reverence is also made before receiving the Precious Blood.
Since the GIRM does not specify what someone is to do if they are passing by but not receiving it is not required to do anything other than continue on one’s way.