The comment above here is great. I'm going to add on. Some of us will feel pressure to speak faster, not hold people up. Let him know it's ok to stutter, it's not a big deal. If he's blocking a lot and struggling, try to just be there with him - maybe give a gentle smile. Think of it like being patient for someone who is learning english as a second language. I always felt a lot of anxiety because I felt like an impediment for other people...