The ear-splitting screech of a knife on a glass bottle has been identified as the worst sound to the human ear by scientists who studied the brain's response to unpleasant noises.
People who listened to a series of 74 recordings while having their brain activity measured by an MRI scanner rated the sound of a fork on a glass as the second worst noise, followed by chalk on a blackboard.
The scans revealed that unpleasant sounds provoked a stronger response in the brain than pleasant ones such as the noise of blubbing water.
While sounds are processed in the brain's auditory cortex, uncomfortable noises activate the amygdala, a separate brain region which processes emotions.
Go here to learn more and listen to some of the sounds that exacerbate our brain: UnpleasantSoundsBrain