He immediately felt bad about it.
With the understanding he found after hugging his chosen rock, he discovered he knew exactly what to do when The Other suggested he “unmake it”.
Without thinking he reached deep into the structure of the rock and made it no-longer-a-rock. At the same time he felt a rush of energy and strength and sparkling thought. It was exhilarating, liberating, and devastating.
Rex had destroyed something. It hadn’t been alive, but it was home to an entire species of organism that had grown there for generations. It couldn’t feel, but its absence left a void that Rex couldn’t fill. Rex had killed before, in his last life - a blaster had often been his only choice for survival, but this was different. He had used his power to connect with an object. It had helped him understand the universe better and he had obliterated it.
The knowledge of it crushed him like the acceleration from escaping Vellegas 6, but without the release of weightlessness at the other end.