The answer can be found in Chapter 22. This is of course when the rising action of the plot is mounting to its climax. Not only is the main plot of the Jacob/Marlena love interest hotting up, but also the subplot of Big Al and his tyranny of the circus is reaching a head too. This of course has been aided greatly by the redlighting of a number of workers over the night. Jacob meets up with Grady who tells him that five of the men who were redlighted (thrown out of the train whilst it was moving) have grouped together and plan to take "Uncle Al down." The fact that both Camel and Walter died during this process of being redlighted has made them want to take revenge on Big Al.
It is therefore this group of men who release the animals during a performance to try and create maximum chaos and to enable them to destroy Big Al and his reputation. The final scenes of this book therefore are largely a description of the ensuing chaos and how the various characters respond.