“Do not curse the king, even in your thought; do not curse the rich, even in your bedroom; for a bird of the air may carry your voice, and a bird in flight may tell the matter” (Ecclesiastes 10:20).
This verse may be fodder for a new version of the Alfred Hitchcock movie, The Birds. In this film all free speech is squelched for fear of birds relaying people's discontent to those in authority with dire consequences.
The author uses humor to get his point across that what we hide in our hearts comes out our mouth often to our own consternation. Jesus taught it is wise to keep a pure heart (Luke 6:45)
