I know, this sounds like advice from some health lifestyle guru.
During my online talk last Saturday I mentioned the importance of having your character breathe.
Particularly during a quiet moment, before he or she begins to talk, showing the shoulders go up and then down again during the exhale/dialogue, adds a tremendous amount of life.
The fact that you can have your drawn character (or CG model) fill its lungs with air makes everybody believe that this is a living being. Breathing is the most basic human (or animal) trait, and is instantly connected to having a soul.
For the most part animating a breath is pretty simple. The shoulders rise, the head moves along, and the chest might come forward. (This pose should last for at least eight frames) Usually the face doesn’t need to face downward, then upward for overlapping action in a subtle move like this one.
It is a good idea though to move the head upward during the exhale to contrast the the shoulders downward motion.
If the sound of the inhale is in the voice track, I would definitely animate it and make it a part of the overall acting. If there is silence, but you have a little pause, I would still try and show an inhale.
You are always looking for moments that add real life, and this is one of them.
Milt Kahl animated these inhales very convincingly within different moods.
Shere Khan is mocking the vultures singing after taking a deep breath.
Medusa becomes furious when she talks to Snoops on the phone.
Wart sighs in respond to Merlin’s encouraging words.
PS. I'll answer all of your questions in connection with the "Virtual Animators" post shortly.