Think about nails scratching a chalkboard for one second. Are you flinching? One study found that this sound literally accelerated the participants’ stress levels, quickening heart rates, heightening blood pressure and even altering the skin’s electrical conductivity. In the study, the scientists discovered that—when stimulated with this screeching sound, the auditory cortex interacted with the amygdala, which controls responses related to fear and emotions.
And if you aren’t near tennis balls on the regular, the scent of the gasoline you pump into your car is more readily available. Some of you reading this are one foot out the door to the nearest gas station, the rest are totally confused.