（修改病句） The plainclothes men noticed a dark-haired beauty slip something into the spy's pocket, when nobody was looking.

（修改病句） The plainclothes men noticed a dark-haired beauty slip something into the spy's pocket, when nobody was looking.

The plainclothes men noticed, when nobody was looking, a dark-haired beauty slip something into the spy's pocket. // The plainclothes men noticed a dark-haired beauty slip something into the spy's pocket when nobody was looking.