Fully Switched to a Second Language?

So, you've lived in another country for some time, speak the other language fluently and have fully switched your mind to the second language. You dream in the second language, you think in it, you do everything in the second language.

Are you sure?

How about math? Counting or doing calculations? Usually, this is one of the fields where we automatically return to the language in which we first learnt it, so normally our native language. The reason for this is that exact math is directly connected to our language centre. While you can evaluate which one of any given numbers is higher or give an approximate result perfectly well in another language, exact calculations as well as counting are unconsciously done in our native language (or the second language which was the first we were taught to count and do calculations in).

What about cussing? Granted, most people learn how to curse in another language pretty soon. But let me tell you a short story: A few days ago, I slipped on the stairs within an Amtrak train, sailed down and landed hard on my arm. The first word which escaped my lips was...German (my native tongue). Although I immediately and without thinking switched to English curse words afterwards, in the first moment of surprise and fury, I unconsciously cursed in the one language in which I had first learnt to speak.

Another situation: You're completely exhausted from lack of sleep, long travels etc. and are just waking up again after having dozed off for a bit. Well, what shall I say: It took me a few moments to realise that the reason why my American boyfriend didn't understand my question was because I was speakind German!

So, you see, there are a few situations in which our brain may unconsciously switch back into our first language although everything else (including thinking and dreaming) is done in the second language. We can't help it; that's just the way our brain works.