When an interviewer’s eyes light up about something or they get slightly animated (meaning what they are saying excites them) that is when you should (subtly) nod in agreement, smile as a response or provide a supplement to their narrative.
They will see you as agreeable, likable, a real team player.
People tend to overdo the above out of nerves, or the want of the opportunity.
Delivering this moderately is advisable.
When they speak to the pain points of the role, what they are struggling with, and what they want you to improve, provide the knowing glance, make them feel heard, give them an example/s of how you dealt with similar problems successfully in a previous role.
Word of caution ⚠️These mirroring techniques have to be understated and used sparingly. If done too much and/or the Interviewer recognizes this as a technique, you will set the wrong impression.
Using these techniques well can make all the difference.