The Poisson distribution is often appropriate in the "binomial" situation of n independent and identical trials, where each trial has probability p of success, but n is very large and p is very small. In this case, the Poisson distribution is relevant for the number of successes, and its parameter (its mean) is np. Discuss some situations where such a Poisson model might be appropriate. How would you measure n and p, or would you measure only their product np? Here is one to get you started: the number of traffic accidents at a particular intersection in a given year.