sperm can only survive outside for 36 hours. In order to survive
longer, they need to be put in somewhere cold?
even the testis regenerates sperm every 2 weeks, the old batch is
then turned into protein and absorbed by the body
chances are she won't get pregnant at all! 
i cannot imagine the sperm still wriggling in the towel after
someone forgets to wash it for 3 days? 
