Here's how it was reported from teh court appearance in other news outlets
"Ms Knox replied: ``I heard she had her throat slit, and from what I saw on CSI, these things are not quick or pleasant, so I said, `Gosh ... bleargh ... this brutality, this death ... bleargh' ... it really did shock me,'' Ms Knox replied.
``It was a disgusting death. I imagined it was a slow death, a death that was shocking, yucky, disgusting"
and
""I heard that her throat had been slit and from what I have seen on CSI, it is not something fast or easy. Blegh," she said, making a gagging motion. "Blegh. It is disgusting. The brutality, to die that way."
I am guessing the report you have linked to have interpreted the 'blergh' part of her statement to be an imitation of the sound.