Or
B) Get impatient, cut them off and tell them everything you know about the topic?
Or
C) Patiently let them finish, THEN tell them you already know, and everything you know about the topic?
I personally have a tendency to be an impatient douche sometimes so I admit I don’t always handle these situations with the greatest patience & social grace.
Depends on if this is work or not.
If it is work and I’m pressed for time, I usually start to interrupt them and give a summary based on what I know and ask them to fill in any gaps.
It can be disorienting for some staff because I can tell that they practiced trying to lay out everything perfectly so that I can understand them and that they have problems trying to parse everything out to create the delta between what they know and what I know.