Kelvin Santos, a two-year-old Brazilian boy, was laid into an open coffin after a hospital declared him dead. An hour before his funeral, the boy got up as if he just woke up from slumber, and asked for water.

Naturally, his family was utterly shocked in disbelief. Twenty hours had passed since the boy was declared dead when he got up.

Antonio Santos, the boy's father, told Daily Mail, "Everybody started to scream... we thought a miracle had taken place..."

However, the boy did not exactly come back to life for long. The family delayed the funeral for an hour, but the boy was buried Saturday as planned.

Then he was 'dead again'

"Kelvin just laid back down, the way he was. We couldn't wake him. He was dead again," Mr Santos said.

The father rushed his toddler back to the hospital, where he was pronounced dead again. He has spoken about suing the hospital for medical malpractice. He believed his son was not given proper care the first time he was admitted for pneumonia.

While Kevin's case is certainly unique, such that he reportedly was able to speak and ask for water, other dead-comes-back-to-life cases have been reported in the past. Some cases were mere reflexes, others were inexplicable even to doctors.

The Lazarus Complex

The body of a brain-dead patient can react after it is detached from a medical ventilator. This is called the Lazarus complex, or the momentary movement by someone pronounced dead. This movement is not known to the brain, as it is only communicated through the spinal cord. It involves the lifting of arms before they are dropped crossed on a dead person's chest. Scientists discourage people from calling it a miracle due to the medical explanation behind it.

Reflex motions have been known to happen in up to 75 per cent of brain-dead patients, but these movements never involved speaking.

According to reports, Kelvin did not simply raise his arms. He got up, and asked for water. How did that happen?

The One Who Really Came Back to Life

In 2008, Velma Thomas, 59, woke up after her respirator was switched off in a West Virginia hospital. She had no heart beat or measurable brain waves. She was even subjected to hypothermia to stimulate her brain in extremely cold temperature. Her family had said their goodbyes before she was taken off life support. When she moved her arm, the medical staff took it for reflexes. And then she began to speak and ask for her son.

Ms Thomas was examined, and full recovery was expected by the time she was seen on Good Morning America.

"There were really no signs she had neurological functions," Dr. Kevin Eggleston told ABC News. He noted, "There are things that physicians and nurses we can't always explain. And I think this is one of those cases."

There was a little of Lazarus complex and a little of Velma's case in the Kelvin Santos story. What could have happened to the boy?