It's a case for linguists around the world. A mystery unsolved. Apparently, there's a word   

no German can ever learn to speak unless German wasn't their first language. This strange phenomenon is richly documented but there's no answer to the question: "Why?"

Below is a clip showing a German girl trying to say "squirrel."

One of the theories states that the use of the crude German language causes severe trauma to a child's tongue nerves which explains why an English speaking person can learn to speak German and still possess the ability to say "squirrel."

Here's what one of the world's most renown linguists, professor Top Gear from Oxford University has to say about the phenomenon:

Whatever the reason for this, the strange phenomenon proves one thing. The German language can cause a vocal retardation and Germans are ugly and so is their language which highlights the fact they constantly get mad.