It's because at that age that's where the most sensitive nerve endings have developed in a baby, and so that's how they explore new things is by the mouth. (crunchydomesticgoddess.com)
He was touching the most sensitive nerve of our Christian existence. (religion-online.org)
That light goes through the transparent liquid behind the lens and strikes the retina, a thin film of light - sensitive nerve cells that line the back of the eye. (scientificamerican.com)