They can be connected to sensors whose sensitivity dwarfs anything a human can do.
The rocks were deceptively sharp and the coldness of the water increased the sensitivity of the soles of her feet.
It is not a seared conscience that's lost all sensitivity.
In a food allergy or sensitivity, when the child eats a particular food, (such as eggs, for example) usually by the time the eggs reach the stomach or the intestines, the body reads the presence of eggs as an allergen (something harmful).
Many people who believe they experience a particular level of sensitivity or prior awareness of events yet to come often seek out psychic tests that can help them determine whether or not those percepions are extrasensory in nature.