habe jetzt mal bei m-w.com nachgesehen und habe folgendes gefunden:
REGULAR, NORMAL, TYPICAL, NATURAL mean being of the sort or kind that is expected as usual, ordinary, or average. REGULAR stresses conformity to a rule, standard, or pattern <the club's regular monthly meeting>. NORMAL implies lack of deviation from what has been discovered or established as the most usual or expected <normal behavior for a two-year-old>. TYPICAL implies showing all important traits of a type, class, or group and may suggest lack of strong individuality <a typical small town>. NATURAL applies to what conforms to a thing's essential nature, function, or mode of being <the natural love of a mother for her child>.
USUAL, CUSTOMARY, HABITUAL, WONTED, ACCUSTOMED mean familiar through frequent or regular repetition. USUAL stresses the absence of strangeness or unexpectedness <my usual order for lunch>. CUSTOMARY applies to what accords with the practices, conventions, or usages of an individual or community <the customary waiting period before the application is approved>. HABITUAL suggests a practice settled or established by much repetition <an habitual morning routine>. WONTED stresses habituation but usually applies to what is favored, sought, or purposefully cultivated <his wonted determination>. ACCUSTOMED is less emphatic than WONTED or HABITUAL in suggesting fixed habit or invariable custom <accepted the compliment with her accustomed modesty>.
Damit wären die Definitionen von usual und normal ziemlich identisch und stützen Sherlocks "definitely wouldn't call "normal" something that "usually" doesn't happen".