First:

I always give my friend a wipe dry with paper because I never know who I will be siting next to on the bus home.

Actually, it's just nicer like that.

Second:

Back in the mid nineties, the BBC website carried a story about a bunch of researchers from a UK uni. They had visited bars in their local area and, whenever they found something like a bowl of salted nuts on the bar, they asked if they could purchase the remaining nuts in the bowl for research purposes.

According to their analysis, in a typical bowl of bar snacks, they could identify traces of urine from around twenty different people on the remaining bar snacks.