First of all, it's really great you're asking this question! I would say not to finish what he's trying to say - unless he asks you to. Maybe he will say at one point "you know what I mean" or "that thing" and point, and then it's of course fine to help him. Key thing is, you seeming impatient will only increase the amount of pressure on the specific word and therefore make it harder to get out. So try not to rush him. I don't think you are, just so you know in the future! About why it's harder to order food than have normal conversation: In small talk, if you feel a stutter word coming up, you can rearrage the sentence or use a synonym to avoid the block. When ordering you *have* to say what it says on the menu. You will sound like an idiot if you say "the opposite of north-east salad" ;) So the added pressure to say a specific word will make it more likely to stutter. Same with names.