Nonverbal behavior is often difficult to interpret accurately, and some people are more skillful than others at accurately decoding what other people are feeling. This is because .

It's ambiguous

Explanation:

Some persons have difficulty expressing themselves using verbal methods. If the individual is familiar with their caregiver it is easy to decipher. But, it is often difficult to interpret one reaction to mean a specific thing since each individual will have a specific and different reaction to the very same emotion, feeling or stimuli.