The process of developing a feeling contact between the mind and parts of the body was described by Ajahn Brahm in his 2021 Vesak address. There it was said the mind already has contact with some parts of the body which are habitually used, but others are obscured, however feeling can be established with any part with practice. Overeating would cause activation of the taste apparatus and the mind would habitually locate to that area, an undesirable response. This primary reaction can be changed by the practice of concentrating on and activating a different part of the body, and the Buddhist recommendation is the breathing. This sensitization is identical with the instruction in the first tetrad:
“3] He trains himself, ‘I will breathe in sensitive to the entire body.’ He trains himself, ‘I will breathe out sensitive to the entire body.’ “—-MN 118
It would be up to the individual what part of the breathing apparatus or body is focussed on and sensitized, but the goal is to investigate (factor of awakening) and establish areas where pleasant feeling is arising as instructed in the second tetrad. The goal is also to get to a point where the mind automatically locates there:
“So let’s focus on the way we breathe. Where do you sense the breath right now? When you close your eyes, what sensations let you know that now the breath is coming in, now the breath is going out? Focus on them. They can be in any part of the body at all, for “breath” here means the flow of energy. Sometimes you’ll sense the breath as the feeling of the air moving in and out of the nose, but it can also be the rise and fall of the abdomen, the rise and fall of the chest. Sometimes those movements send ripples out to different parts of the body, so that you can sense even in your arms or your legs whether you’re breathing in or breathing out. So wherever you find it convenient to focus, focus on the breath sensations there.
Then allow them to be comfortable. In other words, don’t put too much pressure on them as you focus on them. At the same time, notice how long an in-breath feels good. At what point does the in-breath start feeling uncomfortable? Just breathe in as long as is comfortable, and then allow yourself to breathe out. Breathe out only as long as is comfortable, and then breathe back in again. Try to sensitize yourself to what feels good right now in terms of the breathing.
Think of the whole body breathing in, the whole body breathing out, with every cell in your body bathed with breath energy. When you think of the breath in that way, what kind of breathing feels good? You might find, as you start thinking in that way, that the breath gets deeper. If that feels gratifying, fine. If it feels uncomfortable, change the rhythm. Just think, “What would be more comfortable right now?” and see what the body does in response. Think of yourself as hovering around the breath. You’re not squeezing it out; you’re not forcing it in; you’re just staying very close to it, watching it, letting it adjust in whatever way feels good. Give it some space to adjust. Sometimes you might want to nudge it a little bit and see what longer breathing would feel like, or what shorter breathing would feel like, faster, slower, deeper, more shallow, and then notice what happens.”—-Thanissaro