The Two-Headed Dog is a reference to The Twins, the two women who were with Sam when she finally meets back up with the group. The reference appears to be complete when midway through the fight the twin robots are meshed together in a four-legged monstrosity, completing the metaphor of two things in one body. Furthermore, the moment when four-legged twin comes legs-a-whirling at Steven appears to be reference to General Grievous whirling-lightsaber overkill technique he uses when fighting Obi Wan Kenobi. Replace the sabers with legs and youve got an almost identikit image.