Norma reacted as anyone who heard that their guardians had betrayed them would. Her face paled and she shook her head from side to side. Instant denial, which was inescapable.
Who would simply believe the accusation of a stranger that the ones who had been smiling at them all the time could have been waiting for an opportunity to stick a knife in their back?
However, words did not come out of her mouth, for Norma was not an idiot. She knew more of the details than Draco who had mostly used speculation and deduction to fill in the gaps. As such, she had a much greater insight into what Draco had been describing than even he did!
Norma was drowned by a feeling of despair so great that she began to ventilate, despite not being a living being that needed to breathe. Still, she subconsciously needed a way to vent her growing desolation, and mimicking something she would have done were she alive was a sad attempt at doing so.