Google doesn't just listen to words around constantly, they index the sounds you make as well.
Last year I was posting on GFY sitting on my hotel toilet with rancid explosive diarrhea due to a bad clam I had at dinner. Of course I wasn't posting or talking to anybody about this as it was happening but literally as I'm sitting there shitting, after I left GFY to read an article on Drudge Report, I got 2 ads for diarrhea medicine on Drudge Report, one for Kaopectate and another for Imodium A-D.
I wouldn't be surprised if Google hears people coughing a lot that they'll put up ads for cough medicines or list of diseases with symptoms of coughing
