At the very end there are plague flags tied open on each side of the cart. As the cart pulls away the flags are now completely relaxed.
Pete says Alan's blood type is AB negative and so rare that only about 10% chance of finding a donor. AB negative is rare with less than one percent of the population having it. AB negative though can receive blood from people with RH negative types AB, A, B, and O which makes up about 18 percent of the population and thus is almost twice as likely to find a donor than what Pete says.