Why did Riddick poison the dog?

Could you please elaborate on the reasoning behind Riddick's decision to poison the dog? Was there a specific motive or trigger that led to this action? Was it a premeditated act, or was it done impulsively? Were there any consequences to this action, both for Riddick and the dog? It's important to understand the full context of the situation in order to gain a deeper insight into Riddick's motivations and the potential implications of his actions.