Actually we know from where he came; but, where did he go? For those who do not understand the reference, it was a book made and remade into a movie concerning a young man's relationship with a rat.
The question has been posed about what happened to all the sewer and subway rats living in NYC? Did they survive or die: http://www.hlntv.com/article/2012/10/31/rats-new-york-city-after-sandy-possible-outbreak?hpt=hp_c3 If they survived did they move to higher ground and can we anticipate a modern day plague? Well even SciAm, that scourge of LENR, has entered the fray: http://blogs.scientificamerican.com/video-of-the-week/2012/11/01/diving-rats/ Checked your attic or basement lately?
