Open this photo in gallery: Michal Ohana, an Oct. 7 survivor, writes a message to a friend who was kidnapped in the Hamas attacks at the media preview for the Nova Music Festival Exhibition in Toronto.Laura Proctor/The Canadian Press The bullet-holed porta-potties and burned-out cars – all actual artifacts – speak for themselves. But in this exhibition, so do the victims and survivors. Short videos made by festivalgoers at the scene and witness testimonies reveal horror upon horror. Abduct her or kill her? Two Hamas terrorists discussed about a woman they caught, the exhibit recounts. They shot her in the...