The short version
The Trap Door (its own entry, just given), the Secret Smile (a small, private smile used as a maintenance cue), the dial (titrating the feeling up or down on purpose), the Chuckle and Laugh (graded amplification), the Inner Buzz (cautions apply; a felt vibration that arrives on its own with practice; chapter 9 explains how to tell it apart from over-breathing tingle), and finally the release alone, with no exhale carrying it. The book’s central method, taught in full only after chapters 2 through 8 have been earned.
What the research says
The facial-feedback research behind the Secret Smile is real and small: a multi-country study of nearly four thousand people found a posed smile nudges mood by about the lift of glancing at a pleasant photograph. The rest of the ladder is craft, refined over thirty years, with no clinical trials behind it. Cited under Chapter 9.
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.