People approaching death produce a crackling noise that signals they have around 23 hours left to live, a doctor has revealed.

As part of the dying process, people lose their ability to swallow or cough, which stops them clearing secretions in their respiratory tracts, according to the infectious disease specialist Dr Daniel Murrell, from the University of Alabama, Birmingham.

This causes them to emit a gurgling noise with every breath, which may make them sound as though they are choking, according to the Daily Mail.

Although the noise may be distressing for their loved ones, Dr Murrell stresses the death rattle is not painful and is simply part of the dying process.

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The mother of seven-year-old Braiden Prescott, who died from cancer of the nerve tissue in September 2016, woke in the night to hear what sounded like him choking and knew he did not have long left.

What is the death rattle?

Death rattles occur when people nearing the end of their lives no longer have the strength to clear secretions, such as phlegm, from the back of their throats.

This is often accompanied by changes to their breathing patterns, which may vary from very quiet to loud, Medical News Today reported.

Although there is no evidence death rattles cause discomfort, the noise may be eased by turning the patient on their side or raising their head to allow secretions to drain.

Moistening the mouth with damp swabs may also help.

Other signs a person has just hours left include them experiencing:

• Confusion
• Frequent yawning (to draw in more oxygen)
• Incontinence
• A change in odour
• Bruising
• Agitation
• Lost consciousness
• Mottled skin

IS DYING SCARY?

"Dying is less sad and terrifying - and happier - than you think," according to Kurt Gray, the study author of research released in June 2017.

Researchers analysed the final words of terminally ill patients and prisoners on death row to find their thoughts are more positive than you might expect.

They also discovered people often mention family and religion as they are about to pass away, suggesting these ease anxiety as we approach the end of our lives.

Death is inevitable and certain signs indicate when it's near. Photo / Getty Images
Death is inevitable and certain signs indicate when it's near. Photo / Getty Images

The researchers claim their findings should help us rethink how we treat those with incurable illnesses.

Mr Gray from the University of North Carolina, said: 'In our imagination, dying is lonely and meaningless, but the final blog posts of terminally ill patients and the last words of death row inmates are filled with love, social connection and meaning.'

The scientists analysed blog posts from terminally ill patients, as well as comparing the last words of inmates on death row.

IS THERE REALLY A LIGHT AT THE END OF THE TUNNEL?

Last year leading neurologist Dr Cameron Shaw revealed what he thinks happens to people in the 30 seconds before they pass away.

He said we lose our sense of self, our sense of humour, ability to think ahead — all that goes in the first ten to 20 seconds he concluded after dissecting a woman's brain.

Dr Shaw claims there really is a light at the end of the tunnel, but that doesn't necessarily mean life after death.

Rather he said: "We know from experience tunnel vision emerges abruptly when you suddenly lose blood supply to the brain.

"The first thing you notice when you faint is the narrowing of vision, followed by blackness."

He added the last thing a person will think about before they die is their life, standout moments that make it seem as though their life really is flashing before them.

But out-of-body experiences aren't a thing — rather a trick of the mind, he concluded.

- additional reporting news.com.au