Being haunted by evil spirits or experiencing Virgin Mary apparitions are divergent phenomena in many ways. They follow different traditions that are often in explicit opposition, have opposing emotional valence (dysphoric vs. euphoric), one being avoided and the other valued, attract different degrees of public attention, etc. Despite this apparent contrast, the two phenomena are also similar in many ways. They are similar in how individual experience and collective tradition are intertwined and bidirectionally influenced and in how their social transmission depends on the form of a testimony. Using narrative material from my field research in northwestern Slovakia, I will show that the similarities in testimonies about encounters with supernatural agency and the transmission dynamics of these narratives can be illuminated by the contemporary knowledge regarding human perception, memory, and social communication. Psychological insights into when and how collectively shared beliefs and social conventions may influence individual perception or memories show that the underlying cognitive mechanisms are not only associated with uncertainty but are probably direct strategies to cope with uncertainty. I will argue that this creates a specific psychological niche that delineates the forms and enables the emergence of specific narrative traditions in which first-hand testimonies play a crucial role.