Raise his eyebrows
Have you ever met a man raising his eyebrows when talking with you? Eyebrows are important parts to show one's facial expression. When someone is surprised or flirtatious, he/she is more likely to raising eyebrows. It shows that he is interested in what you talking about.
Open his mouth
We may open out mouth when we are surprised. If your trans dating partner is open his mouth while you are speaking, it means he is listening what you are saying carefully, or he is interested in what you are talking about. You can share some interesting things with him at this moment.