"Hey, Rube!" is a shout out that was originally used by people who worked in a circus. It means that there is an emergency situation or a fight happening and everyone needs to come and help out.
To explain it simply, imagine you are playing with your friends at the playground, and suddenly someone starts fighting. You would shout "hey, friends!" to tell everyone to come help break up the fight or see if anyone needs help.
In the circus, "Hey, Rube!" was used to call out to all the performers and workers to come together and handle any conflicts or dangerous situations. It was important for everyone to work together and keep each other safe.
So, "Hey, Rube!" is a call to action when something difficult or dangerous is happening and people need to come together to help each other out.