A dancing monkey is an accomplice who follows the leader (silver back) at all times, through thick and thin much like an urchin except acts more like a master's puppet.
The dancing of rage as the coin drops in the "slot" and the monkey jumps to life.
As he bent over, his plumber's crack was glaringly obvious, so I took out a 5c piece and dropped it in the "slot" (his crack) and jumped back shouting loudly, "Dance Monkey, DANCE!" and so is born the dancing monkey!