Teaching a language on accident It happens. You become so single minded about something that other people start noticing. 
I have been studying Japanese on my own. One of the ways I do this is by reciting vocabulary lists while I work. 
One day a co-worker said something to me in Japanese. When I asked him how long he has been studying the language, he said he wasn't. He had learned it from me. 
Apparently I talk to myself when I study. Has anyone else had an experience like mine?