The short version
Open the throat (the shape just before a yawn), soften the jaw and tongue, and take the air in over two or three seconds; then any of the paced or box-breathing patterns, run silently enough that nobody else in the room can tell you’re doing anything.
What the research says
Craft, from a job where a microphone hears a swallow.
Rooms where it does the work
Two rules, no exceptions
Never practice any technique on this site while you are driving, operating machinery, or doing anything that needs your full attention. The slow ones can make you drowsy, faster than you’d expect. And never practice a breath-hold, bellows breath, or any vigorous breathing in or near water. Read Before you begin for the doctor’s list and the rest.
The short version is a reminder, not a lesson. The chapter has the story, the steps, the mistakes, and the limits.