It is true that, etymologically, Zwieback and Biscuit are exact correspondants, yet here in Switzerland, they are well-distinct items on the bakery shelves. "Zwo" is used in Swiss dialects besides "zwei".

Thanks, Werner. I was confident that you would be able to come to my rescue on this one, even though I think Schweizerdeutsch sounds as much as like Hochdeutsch as does Cantonese!