When you get anxious or emotionally aroused, you sweat. Not a lot, but enough to be detected using electrodes on the finger tips.
And it turns out that if you take a bunch of atheists, and get them to dare god to do horrible things, they get sweaty.
A team from the University of Finland got 16 atheists and 13 religious people to read aloud statements like "I dare God to make someone murder my parents cruelly" and "I dare God to make me die of cancer".
Via Ben C. O. Grimm