Literal Translation
… curious nose mustard pot?!
Actual Meaning
Nosey, busybody
Etymology
🇧🇪
Ok I fell into a rabbit hole…
“curieuse neuze: someone who is very curious, immodest” (Ghent), “kerjeuzeneuze: a very curious person” (Oosterzele), “kerjeuz-neus: a curious person” (Asse), “krejuizenuis: a very curious person” (Brussels), ‘curieusche neus; inquisitive’ (Ronse), “curieuscheneuze: curious (man or woman)” (Kortrijk), “kreuzeneuze” (Lokeren), “krejezenees” (Okegem), etc
BUT it seems the general vibe is: a curious nose will encounter a mustard pot/jar, which would be unpleasant! Often said to kids who are eavesdropping on grownups.