Appetite comes back before anybody announces it. One afternoon you want a specific thing — toast, a proper cup of tea, something salty — and the wanting itself is new.
Nobody records that in a file. There is no test for it.
But people who have sat beside a bed know it as the first real signal, and it usually arrives well before the numbers move.
The body posts these notices without waiting for permission or evidence. The smile is downstream of that. Not a technique — just what happens when something quietly reports that it is still in business.