Kotowaza of the day: Should be seen and not heard?

Japanese:

黙り虫壁を通す

Romanized:

Damari-mushi kabe-wo toosu

Meaning of Japanese:

Quiet bugs (worms) bore holes through the wall

English equivalent:

Still waters run deep
Beware of a silent dog and still water (and a still enemy)
Never trust a tailor that does not sing at his work (, his mind is of nothing but filching)