Our skin conducts electricity more or less efficiently, depending on our emotions. We know that when we're emotionally stimulated ─ stressed, sad, any intense emotion, really ─ our bodies sweat a tiny bit, so little we might not even notice. And when those tiny drops of sweat appear, our skin gets more electrically conductive. This change in sweat gland activity happens completely without your conscious mind having much say in the matter. If you feel emotionally intense, you're going to notice an increase in sweat gland activity. This is particularly useful from a scientific viewpoint, because it allows us to put an objective value on a subjective state of mind. We can actually measure your emotional state by tracking how your body subconsciously sweats, by running a bit of electricity through your skin. We can then turn the subjective, subconscious experience of emotional intensity into an objective number by figuring out how good your skin gets at transferring an electrical current.