[joefourier]

Why, instead of the probability being 0 or 1 in a quadrillion, is the probability not simply undefined?

Maybe I am not well-versed in Bayesian thinking, but I am unable to understanding assigning probabilities to events that have not occurred before, and to which there is no related numerical data.

Making the probability of Pascal's number being undefined renders any calculation of the risk involved null and solves the problem, while making it possible for future evidence to assign a defined probability (say you were previously approached by 10 Pascal's muggers and 2 turned out to be telling the truth).