The explosions were happening in a series, so Kakashi had a way of knowing what would happen next. He knew it from the calculations he did in the little time; at which, Onogi just laughed.
He was sitting in a dark room with glowing hologram screens around him. "Took you long enough, bastards," he had said when they had arrived.
Then Hitori got close to the stairs, he had seen the dynamites. Onogi was sweating, he thought about pressing the button and blowing him – but his plan was to take as many as he could, so he waited.
Then, suddenly, they became aware of the trap from something they talked about on their stupid wand – that bitchy piece of wood. Onogi clenched his fists. He knew someone had told them about the dynamites. But who? No one knew except his father and him.