germs ;)
There is a good advice for all those people who are interested in the monthly new BVG-magazine (BVG = public transportation company in Berlin): Do *not* take a magazine from the middle of the magazine-holder - everybody does that already.
Yes, we probably all believed that the magazine in the front is the one that many ppl already took out just to put it back in place after reading it a while - and that this is the one with the most germs on it. But I got news for you: On my many drives with streetcars, busses etc. I watched so many people following this rule - taking a magazine from further on in the row *and* putting it back in the same place even - if they did not want to take it with - that I believe now that the cleanest one sits directly in the front cause thats the one that no one wants.