Answer:
Step-by-step explanation:
The fact that you are whispering is not part of the information you are trying to convey. It is a very strong hint of how important it is not to let someone else hear what you are communicating.
The idea is that it is a secret and you don't want it shared. You don't want to tell anyone nearby what you are saying.
It is non verbal because it is not part of the information itself. It is your attitude about the information that is being conveyed.