It sounds like you're starting to make a point about the power of body language, but your sentence isn't quite complete. Body language indeed plays a significant role in communication, often conveying emotions, attitudes, and intentions that spoken words alone might not. It can be considered a "quiet secret" because it operates mostly below the level of conscious awareness.

To finish your thought, you might consider something like:

"Body language is the quiet secret and most powerful form of non-verbal communication, often revealing more than words ever could."

Or perhaps:

"Body language is the quiet secret and most powerful tool in interpersonal interactions, subtly influencing how messages are received and interpreted."

Feel free to adjust based on what aspect of body language you'd like to emphasize!