When the boys hide inside a small room within a tenement building, who first detects approaching danger and leads the other two boys out through the hole in the roof to safety?

When the boys are spending their time in a small room inside a tenement building and have made a hole in the roof as an emergency escape route, they are sitting there one day when Rat detects some changes in sound within the building. He notices that the woman and her children who live downstairs are suddenly unusually quiet and he then hears footsteps upon the ladder. Recognizing the danger, Rat then leads Raphael and Gardo out through the hole in the roof to safety.