In this paper I will study the use of two rare words in Origen’s 'Against Celsus', κατάκλησις and κατακαλέω. After a short survey of the corpus (one occurrence in Celsus’ 'True Discourse', six in Origen’s text), I will show that the unusual frequency of these words in Against Celsus is patently linked to the presence of κατάκλησις in Celsus’ text: this could shed new light on Origen’ apologetic strategy. I will then discuss the meaning of these words in Against Celsus. Both Celsus and Origen use κατάκλησις and κατακαλέω to speak about magical rites involving demons – which is unprecedented in previous literature. Nevertheless, some occurrences of the word κατακλητικός in magical papyri and in a tabella defixionis could provide an explanation of this peculiarity.