A simple experiment: put a person in a tube. Add a snake. Details are reported in the study [and click on the image here to see the video that accompanies the study]:
“Fear Thou Not: Activity of Frontal and Temporal Circuits in Moments of Real-Life Courage,” Uri Nili, Hagar Goldberg, Abraham Weizman and Yadin Dudai, Neuron, Volume 66, Issue 6, pp. 949-962, 24 June 2010. The authors, at the Weizmann Institute, explain (and also present video of):
In this study, volunteers who fear snakes had to bring a live snake into close proximity with their heads while their brains were scanned using functional magnetic resonance imaging (fMRI). Bringing the snake closer was associated with a dissociation between subjective fear and somatic arousal.