When you're first starting out, I think your brain is trying so hard to make any sense of the language, that it picks out any vaguely resembling words that it can string together to make a proper sentence. Then, once you think you've heard a word, it's very difficult to unhear it.
It's my experience that this is something that works itself out with exposure to the language, and that most of our students start to reliably distinguish between the Norwegian vowel sounds around level 8-10, even if they struggled with it initially.
This one probably comes from the 1982 film 'The Thing'. In it a Norwegian man warns a group of people that the dog they are all hugging is an evil Thing and not actually a dog. Except they don't understand Norwegian!
Though he uses a different word for dog: 'bikkje'. "Det er ikke en bikkje!!"