As a fan of Seinfeld, I thought that this study was entertaining and informative. It turns out that double-dipping a chip really IS like putting your whole mouth in the dip.
The Seinfeld reference comes from an episode in which George goes to a funeral, and one of the other people there is aghast that George dips a chip, takes a bite, and then dips it again. This study found that “sporadic double dipping in a cup of dip would transfer at least 50 to 100 bacteria from one mouth to another with every bite.”
So there you go. In related news, this same researcher, who works at Clemson University and apparently has made a bit of a hobby of exploding popular myths, published a study last year on the five-second rule. The results? I wouldn’t eat anything off the ground, if I were you. Especially if it is a large piece of meat that drops out of your gyro late at night while you are standing at one of the most heavily-trafficked tram and metro stops in Prague. This may sound hypothetical, but it has already happened once. So if you find yourself in that position, you know what to do.
Elliot Ritzema 
Oh my gosh, I would NEVER pick up food off of European ground and eat it.
Your nephews have no problem eating stuff off the floor – I’m hoping it builds their immune systems.
I re-thought this answer the other day and realized that it may have sounded like “European ground is so dirty, so I’m going to continue throwing food onto American soil because it’s better.” Wasn’t what I meant. In case anyone was wondering. All ground is pretty gross. 🙂 But I was remembering Kobanya Kispest (veg allomas) with my earlier answer, which is probably the scariest place to eat food anyway, whether it’s on the ground or not.
Dawn, I smell what you’re cookin’. My experience of Europe has basically been the same as yours: urban, and kind of dirty. Sure, there were trips out of the city from time to time, but most of my time in Europe was spent in Prague 6 or 10, or scenic Kispest. They have their own charm, but I have yet to see a tour book with a picture of them on the cover.
And thanks for adding the (veg allomas)! Yes, the Kobanya-Kispest metro station is a scary place to eat food, or even just BE at certain times of the day.