窍 (w)

(qiào) intelligence; opening; tunnel to the heart (traditional concept)

窍门 (w)

(qiàomén) a trick; an ingenious method; know-how; the knack (of doing sth)

窍门儿 (w)

(qiàoménr) a trick; an ingenious method; know-how; the knack (of doing sth)