She spoke in the "tone" couples often complain about in my office. He replied, and it was below my hearing level. She said something else in the same tone and I saw him throw both hands up from the elbows. Then they were out of sight.
Begin to notice the couples you see. What tone do you hear? What facial expressions or body language do you notice? Does someone roll their eyes at the other (showing contempt)? Do they face toward or away from one another? Does one dominate the conversation?
You can see this through car windows, cafes or restaurants, or as you walk down the street.
Of course, eventually, I want you to begin to notice your tone and body language with your mate. But be an observer for a while first.
Let me know what you see.