My theory is that the circus just goes from town to town giving some people the pink ticket, which leads them to the pink tent in which they are druged and latter used in the shows in a similar way as the person we saw getting a knife in the head; and once they have done enough killlings they move to a different place. Also, i may be wrong, but i belive that the actors have been cursed after having killed -and probably eaten- the angel with an inmense craving for human meat, so they may eat the pink ticketed visitors.