That’s the tough part there is nothing you can do to make them feel better. The time pressure they are under to speak when spoken to or answer questions when asked causes them to stutter, as we tense up and the words don’t come as planned. As a stutterer I know it’s uncomfortable for the listener which just makes the whole situation worse. Which is why stuttering can be so brutal and we avoid speaking situations all together to just no deal with the heart-ache and making situations awkward. I would just say at least act like you’re listening still. Sometimes it feels like people become distracted or quit paying attention or look away. Sometimes people finish what word I’m looking for which I know some stutterers say never to do but I don’t mind personally as it helps speed along this speaking situation. Just listen