I've heard that about animals sometimes.
But then nurses can also tell from reading the body and vitals how long someone has left. I remember in one of the above cases when the family were asking if they could leave the person for a little bit they were told they could but not to make it more than about twenty minutes. They were monitoring the systematic shutdown of the body. Apparently the body shuts down in order at death, so once they see the sequence begin, they can generally tell when the next system will stop, then the next and so on until death.
Just like how the body starts up at the beginning of life. There's an order to everything.
'If the Apocalypse starts, beep me!' - Buffy Summers
'The sky's the limit.....' Jean-Luc Picard, 'All Good Things'
courtesy of Saquist