It was a conception of Heron of Alexandria depicting Hercules launching an arrow against a dragon that hissed when being hit.
If the viewer of the automaton raised the apple that laid in the middle of the platform then, by the concealed chain, the hook in Hercules’ hand was released and the arrow was launched while the valve, which obstructed the bottom of the upper container, was raised and the water penetrated the intermediate container forcing air to leave the built-in tube of the dragon giving a sense of death’s hiss.