壁に耳あり障子に目あり

[kabe-ni-mimi-ari-shouji-ni-me-ari]

Literal translation:

Walls have ears, and sliding paper doors have eyes.

Meaning:

Someone may be eavesdropping and peeping. (Secrets leak easily.)

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障子 [shouji]: a Japanese traditional sliding door/screen composed of a wooden frame and paper.