The odour of sanctity, according to the Catholic Church, is commonly understood to mean a specific scent (often compared to flowers) that emanates from the bodies of saints, especially from the wounds of stigmata.
In the absence of carefully written records, either by or about the individual, evidence of a saintly life was attested to only by personal recollections of those around him or her.
There is a theory that the odour of sanctity is due to the smell of acetone and/or acetoacetic acid, caused by ketosis brought on by starvation from fasting.
Saint Thérèse de Lisieux (a French Discalced Carmelite known as "the Little Flower") was said to have produced a strong scent of roses at her death, which was detectable for days afterward.
At the moment Madame Elisabeth was guillotined "an odour of roses was diffused over the Place de la Révolution" where she met her end.