podmuklo

1. (of people) treacherously; deceitfully; sneakily
   Podmuklo ga je napao s leđa. — He treacherously attacked him from behind.
   Podmuklo se smeškala dok je lagala. — She smiled slyly while she lied.
2. (of illness, danger) insidiously
   Bolest je podmuklo napredovala godinama. — The disease progressed insidiously for years.