The Adventure of the Clapham Cook - S1-E1
Hastings: It's a wonderful day. Just fill your lungs with that air!
Poirot: No, my poor friend, this sort of air is intended for birds and little furry things. The lungs of Hercule Poirot demand something more substantial: the good air of the town! (00:26:00)
Answer: He definitely says "Belgian", but the subtitles get it wrong and show him saying "American."
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