Act like a sounding board

 

show that you understand what the other person just said, like: You mean..., or: If I understand you correctly,...  Magnify what was just said.  Everyone wants to be listened to.  (He is an intern there, he should listen first and more. A mentor may have the patience to listen to what an intern has to say. Others, not much.)

It's also a chance for him to add his own thoughts.

The difficulty he experienced stems from he was subconsciously waiting for the moment everyone is looking at him for his words.  During one-on-one, that's when he'd speak.  In a group meeting, that's not going to happen.