Imagining the cartoon is talking about an interesting Japanese Saying.
If you translate it from words to words, it’s saying "Walls have ears. Doors have eyes". It’s not so hard to guess what it is trying to say if you knew the 「Kanji」.
The saying is telling people who need to take caution when they are talking about something secret or confidential. People don't even notice someone is behind the door / wall who can hear what they are talking about which might cause troubles.