Remember that you are mirroring and matching your partner. Practice, practice, practice
Then add a new aspect.
Clenching your jaw and other skin tightness can be easy to notice and might be harder to imitate.
Go through the previous exercises and be in touch with each other. Build rapport naturally by doing these things. Seriously, today, I am asking you to try all the previous ones.
You don’t even need to talk. Sometimes just watching a movie or tv or concert or sports etc and match them and they feel closer to you, if you are skillful.
Imagine what is going to happen with your connection if you are motivated to practice.
If you choose not to practice this with your partner, knowing that they feel closer doing this, what message does that send?