When it comes to a metzorah, the live bird is dunk in the blood of the dead bird and sent away over the field. Maybe, the chirping of a bird reflects speech. There is good, allowed speech and bad, forbidden speech. The Kohen, being responsible for teaching proper behavior, is limiting the good speech not to come to bad speech by the dunking to show that we are killing some of it off and then the bird can fly freely over the field, one is free to speak.
