Sara Nir was up late, checking her email when she heard knocking sounds that went from a soft tapping to hard pounding to a frightful crash overhead — as if a wall had collapsed in the unit above her ground-floor condo. Sara Nir was up late, checking her email when she heard knocking sounds that went from a soft tapping to hard pounding to a frightful crash overhead — as if a wall had collapsed in the unit above her ground-floor condo.