"We would hear the sound of the blows," says Sister Tobiana Sobodka, who was in the next room to Pope John Paul II at his summer residence in Castel Gandolfo, near Rome.
Her evidence was given to the Vatican body which is considering whether to declare the Pope - who died five years ago - a saint.
Flagellation is the beating or whipping of the skin, most often on the back, and often drawing blood, as a bodily penance to show remorse for sin.
It was a widespread practice in some parts of the Catholic ministry up to the 1960s but is uncommon today, says Professor Michael Walsh, a Catholic historian
But in some countries like the Philippines, this re-enactment of the suffering of Jesus Christ - called the Passion play - can take a more extreme form and can draw blood.
It is thought to have come to prominence in Western Europe in medieval times around 600 to 800 AD as an extreme version of bodily penance, says Professor Lewis Ayres, a Catholic theologian at Durham University.
http://news.bbc.co.uk/2/hi/uk_news/magazine/8375174.stm