Whilst Seth was talking with Rania, congratulating her on helping him with his discovery and giving her a gift for inspiring this revelation, a small part of his mind was still in control of Corvus.
It always was, at this point, his mind had grown strong enough with all of his evolution that, in the state he was now, Seth was essentially living two lives. He had grown so used to living life through two sets of eyes, that he genuinely had trouble remembering when it wasn't like this.
So when something strange appeared in the corner of Corvus' eye, Seth didn't even blink as his separated mind turned its attention to this sight. It was this ability to exist both inside and outside of the shop at the same time, that Seth was able to see the colossal boulder careening through the air towards them like a run away train, thankfully spotting it before it crushed them into paste.
