Final answer:
The pivotal event initiating the story's action is McTeague's attempt to fit a billiard ball into his mouth, which escalates into a dire situation when he cannot remove it.
Step-by-step explanation:
The event that sets the story into motion in the provided text snippets is when McTeague is challenged to put a billiard ball into his mouth.
This event occurs when Marcus, wishing to see McTeague's ability to open his jaws wide, passes him the ball, leading to McTeague's attempt, which turns into a serious and distressing situation when the ball gets stuck. The ensuing chaos and panic, including the barking of the four dogs and the gathering crowd, drive the story forward.
The event that sets the story into motion is when the Moose decided to go public with his hang-up. This event leads to the crowd chanting, 'Give the Moose the ball!' which creates a turning point for the story. It signifies the Moose's determination and his desire to show his skills and abilities to the public.