With accent marks:
В ти́хом о́муте че́рти во́дятся.
In a quiet whirlpool, demons live.
This proverb usually characterizes an unremarkable, inconspicuous person who suddenly turned out to be capable of extraordinary acts, not always good.
The proverb comes from the old Slavic beliefs, according to which the whirlpools are the habitat of water demons and evil spirits. It was believed that they were the ones who dragged swimmers to the bottom.
The English analog of this proverb is "Still waters run deep".
Other Russian proverbs
Eggs don't teach the chicken.
The quieter you go, the further you'll get.
Fear has big eyes.
Crowded, but not aggrieved.
Start taking care of the dress while it's new, and of your honor while you are young.
Without labor, you can not even catch a fish in the pond.
We don't appreciate what we have but we cry when we lose it.
Оne sees the mote in another's eye and ignores the log in his own.