"Dirty Ice Cream"

I always wonder why is our ice cream,you know the one we buy from the street from the “sorbeteros” when we were young and some are still now(I stopped eating it because one of our pedia patients are admitted due to typhoid after eating dirty ice cream,maybe it was just a random chance that the patient got it, a 1:100 ratio maybe),are called “dirty ice cream”? Its not that its dirty or something,right?Then a friend recently told me,”because of how the way you eat it,you idiot!It took me atleast 10 seconds,Oh God Im too slow,then I got it,and I was laughing really loud!(can you see the similarities from the photos?haha)

(Images are taken from yahoo.com)