Dog only eats the right side of his food.. Why?

Is this just.. a thing? This is Apollo. He does this almost every meal time. He’s a rescue, got him when he was 1 and a half. He’s 5 now, but he’s always done this odd behaviour. He’ll go back and finish the rest later like, but anyone any ideas or seen this before? Why is it exactly half?

Is this just.. a thing? This is Apollo. He does this almost every meal time. He’s a rescue, got him when he was 1 and a half. He’s 5 now, but he’s always done this odd behaviour. He’ll go back and finish the rest later like, but anyone any ideas or seen this before? Why is it exactly half?