Differences between nel and nello?
They're both compounds of "in" with a definite article, so they follow the same rules as the articles, i.e. "nel ristorante" because of "il ristorante", and "nello zoo" because of "lo zoo".
...and turns to the bun and says...
is nella a word?
Yes. There is a nice table here: http://italian.about.com/library/fare/blfare153a.htm
grazie,questo è stato molto utile
The sausage is in the restaurant? It seems that the meaning doesn't really matter?