Some people who experience a religious conversion seem to undergo a personality change. They can be quite congenial and easygoing when talking about mundane things, but when they start talking about their faith, their demeanor changes. Their tone of voice modifies, their smile becomes tense and they become defensive when questioned about their evidence for belief. It becomes difficult to have a friendly conversation with them.

The God Virus: How Religion Infects Our Lives and Culture (ed. Ipc Press, 2009)