Collocations for sinister - adj.

be, look, seem, sound
find sth

extremely, fairly, very, etc.
deeply, truly
almost
a little, slightly, etc.
faintly, vaguely
I found his silence faintly sinister.

somehow

Sinister is used with these nouns:
aspect, connotation, design, grin, implication, laugh, laughter, motive, shadow, undertone, underworld