Well you need to assign your own probability, we can never know how many @#$ burgers have been served domestically, 1% is high.
If McD serves 3 burgers per minute and is serving burgs 12hrs a day, they are serving like 15,120 burgers per week. You gotta assume one nutcase is spanking it into a burger each week, probably on a Friday night, he wanted to play D&D with his buddies but Milton called in sick and he had to cover. I think that .00006613 of burgers have spank in them and I think that on Friday night .000231 contain spank.
The question is, do you feel lucky?