Profanity has attracted much scholarly attention for the reason that swearing, oaths, and insults “manifest language use in its most highly charged state” (Taavitsainen 1997: 815). This article examines the possible functions of swearing per membra Christi [by Christ’s limbs], starting with a particularly revealing example from a group of late medieval pedagogical dialogues, the Manières de langage . Taking the perlocutionary reaction to this utterance as a starting point, the wider phenomenon of swearing on the body parts of Christ in both Middle English and Anglo Norman will be explored. This behaviour was initially conceptualised (and widely condemned) as an act of blasphemy, the notion of dismembering Jesus being especially widespread. However, this article also concerns itself with the emotive interjectory function of swearing oaths on God and Christ, and will posit that this behaviour is caught in a long process of pragmaticalisation during the high and late Middle Ages. This research supports the view of a bidirectional channel of influence between Middle English and Anglo Norman, and suggests a similar trajectory of both pragmatic development and language attitudes.