And though you don't often find them in beginners' German books, they do have a major upside for language learners: a well-placed interjection or exclamation can help you express yourself to whoever's around, and can easily cut through any language barriers that may exist. Primarily, you'll use it to express surprise or disbelief - it's a great interjection to use when your friend is telling you a shocking or unbelievable story, for example, or if someone surprises you by making a thoughtful gesture. For example, if your friend tells you there's a rail strike on the day you plan to travel on holiday, an "ach, nee" can show your disappointment at the news.