So whenever there is an empty seat on a crowded train there is a reason. Usually something or someone foul, sometimes both. This time it was both but only the something remained.
It took the form of some soggy papers on a seat sopping up what looked to be a small pool of urine.
Interestingly enough all the adjoinning seats were occupied and everyone seemed to be ignoring the little patch of fowlness. Now I know logically that the pool cannot attack, and it looked to shallow to even spill or splash over, even with some train turbulence. But I still felt the need to keep some distance.