Symbolism, Imagery, Allegory
Just Plain Evil
There are complicated symbols in this world, Shmoopers, and the claw stick ain't one of them. This terrible contraption is a symbol of torture and abuse, and represents the callous disregard that people who use them to train animals hold for the animals they're training.
Insofar as the claw stick is more like a weapon than a tool, then, it is also a symbol of powerlessness. The animals held in captivity are at the mercy of the people who own them, certainly, but the claw stick also represents how powerless the people feel when confronted with something bigger or more powerful than themselves. Since the claw stick references powerlessness on both sides, then, it also underlines the absurdity of keeping wild animals in captivity and making them perform in the first place. It's no good no matter how you slice it.
When Mack uses the claw stick in Julia's presence, he claims he's only using it get Ruby's attention—but when it comes down on Ruby's head, it's clear that he isn't telling the truth. And when this happens, Mack gets demoted from clueless boss to animal abuser. For more on Mack and where he falls in the whole good-and-evil debate, be sure to read up on him over in the "Characters" section.