The present article examines the meaning and function of olfactory remnants, often repugnant, linked to demons in the context of late medieval witchcraft and demonology. This reflection is developed within the framework of a «make believe» logic sustained by the doctrinal, theological, narrative and judiciary constructions of the witches' Sabbath. Incorporated within the order of sensory perception, references to the fetid smell of demons - who are by nature devoid of odour because they are pure spirits - constitute further proofs bearing witness to demonic presence, and thus testifying to the ignominy of the crime of witchcraft and to the guiltiness of the accused. According to those who attacked demon worshippers, the devil truly revealed himself physically; human beings were able to touch, hear, see and smell him. Sensory faculties were therefore perceived as being instrumental in corroborating the existence and reality of the Sabbath and the presence of the devil in bodily form. These considerations bring us to examine the olfactory fields associated with the devil's odour: odour of corpses, hell, sin, deviance, but also of defilement, impurity, corruption and excrements. These fetid odours are embedded in a logic of moral, spiritual and religious inversion of positive odours, such as the «sweet fragrance» of the saints, the «pure odour» of Christ or the «soft perfume» of virtue.