When the horse walked into the tavern, the barkeep asked, “Why the long face?”
A very old joke in English, is it well known in Italy too I wonder?
According to WordReference, the expression “a long face” becomes “un muso lungo” in Italian.
So Italian and English use the same expression in this case, that’s interesting.
“Faccia lunga” and “muso lungo” can be used interchangeably.
“Muso” is properly the “face” of an animal, but it can be used, mostly in disparaging sentences, in place of “faccia”.
Since we are talking about “long face”, and “muso”, I’ll add that “Tenere il muso” is another expression that can come handy.
It means “to act sulky”, “to act offended and silent”.