Only very sharpest vision could spot this hidden killer as it lies in ambush.

就是说只有非常尖锐的眼睛才能发现这些潜伏着的杀手。

youdao

"We feared demolishing the building and disturbing the soil could release this hidden killer again, " he said.

BBC: Former Turner and Newall factory

But in many Asian and African countries, the indoor use of coal and biomass fuels for cooking and heating is a hidden killer.

CNN: Air pollution kills, but deaths can be prevented

Studies suggest social isolation is associated with a higher rate of death in older people and loneliness is the "hidden killer" of the elderly.

BBC: Is modern life making us lonely?