Obviously they have listened intently to the speaker. Time and again as the next person and the next, and the next tries it, and they get it wrong, they get more frustrated. Let the game go a while and gradually emphasise the thing they are missing, the cough. Even exaggerated, even hyped to the heavens and over-acted, it will be missed. Writers must edit.
Dialogue is an illusion.
First a stripping out, a tamping down, and then a zipping and zapping up, an enhancing of everyday speech, until, while we wallow in the fictive dream, we feel and hear the characters, more alive, more real, more exciting and interesting. There is no need to be exact to represent the truth. The same goes for dialect. If we are in our own environment we don't hear dialect and accent, we LIVE dialect and accent. Like the man who didn't know he'd spoken prose all his life, colloquialisms are often taken for granted and often unnoticed.