 In the two-factor theory framework, an unusual event is responsible for the formation of the delusion. The young woman who thinks that her father has been replaced by an impostor would form this belief because she has reduced autonomic response to familiar faces (factor 1), and this affects her capacity to recognize the face of the man in front of her as her father’s face, even if she can judge that the face is identical (or virtually identical) to that of her father. But this unusual event (due to a reduction of autonomic response) is not the only factor responsible for the formation of the Capgras delusion. In order to explain why the thought that a dear one has been replaced by an impostor is adopted as a plausible explanation of the unusual event, a factor 2 is required, and this can be deficit at the level of hypothesis evaluation (Coltheart 2007), or the presence of exaggerated attributional or data-gathering biases, such as the tendency to ‘jump to conclusion’ on the basis of limited evidence (Garety and Freeman 1999). In a more recent version of the two-factor model, the problem is no longer identified with the adoption of the delusional belief, which is described as the best explanation for the unusual event. Rather, the problem lies with failing to give up the delusional belief in the face of overwhelming counterevidence after its adoption (Coltheart et al. 2010).