Respectfully acknowledge their verbal comments and their non-verbal responses. And use these to adjust what you say and how you say it. A major tool in avoiding misinterpretation is to pay attention to the other person's non-verbal responses to you. Go for the totality of small clues from their eye contact pattern, head nods, gestures, voice tone, etc. The changes are subtle but they are there to see if you watch for them.
Pupils contracting often indicates disinterest.
They can often be involuntary releases of tension. Precisely what they mean will depend on the situation and on the person with whom you are conversing but, as an example, small jerky movements can often be a sign or disinterest, irritability or impatience. 2-way communication Paying attention to all of these while also speaking and listening requires that your full attention is on the other person and on how they are responding and are continually adapting and adjusting how you communicate to ensure they fully understand you. This is 2-way communication. You are being responsive to the other person, instead of talking at them, and are ensuring that what you say is being accurately understood.