According to the third edition of the Shorter Oxford Dictionary, an interjection is a grammatical term "expressing emotion, viewed as a Part of Speech." Wikipedia describes an interjection as "a word or expression that occurs as an utterance on its own and expresses a spontaneous feeling or reaction" that furthermore "partly overlaps with categories like profanities, discourse markers and fillers."
In German too, some interjections are also standard nouns, but most are basically sounds that express emotion. Here are some examples of German interjections that are nearly identical to English:
Ach, jetzt weiß ich, warum wir verschlafen haben. -Aha, warum denn?
Oh, now I know why we overslept. -Aha, why then?
Caption 53, Die Pfefferkörner - CybermobbingPlay Caption
The next one is pretty easy, because even though it's spelled differently, it sounds the same:
Sonst gibt es keine Krone. -Autsch!
Otherwise there won't be any crown. -Ouch!
Caption 8, JoNaLu - Prinz Dreckspatz - Part 2Play Caption
The more common expression of pain in German, however, is aua, which is similar in sound to the English "ow."
Bingo, wir sind im Geschäft!
Bingo, we are in business!Play Caption
„Es ist schön, dass wir in Deutschland sind." -Bravo.
"It is nice that we are in Germany." -Bravo.Play Caption
There are also many German interjections that sound entirely different from their English counterparts:
Ich bin... was, "short"? -Ach, ich bin klein!
I am... what, short? -Oh, I am small!
Caption 15, Deutschkurs in Tübingen - ObwohlPlay Caption
Na ja, wer's glaubt, wird selig.
Well, he who has faith shall be blessed.
Caption 12, Großstadtrevier - Von Monstern und MördernPlay Caption
Mensch, wo bleibt sie denn?
Man, where is she then?
Caption 25, Die Pfefferkörner - EigentorPlay Caption