I read a narrative where the author was talking about her childhood. She said that one day she and her father, a brother and a sister were inside the car, the kids were eating popcorn and drinking cream soda. Someone said something funny at the very same moment in which she was drinking the cream soda. As a result she aspirated the drinking and choked. The situation got pretty serious, but after a while she recovered. So, her brother asked: "Did it go down your windpipe?" She replied: "I don’t know—I don’t know what happened". Her father answered: "Probably". And her six-year old asked:
Did it go down your muffler?
What does the word "muffler" mean in this contest? And, why is it funny? I know it's something funny, because she said that it made everybody start laughing again.