Caio heard the sound of the main gates closing behind him as he walked out of the imperial prison. He didn't know what exactly prompted him to consider Concubine Number 19's speculation. After all, the evidence clearly pointed at her; having the vial in her room was more than enough proof to get her sentenced to execution. But instead of doing that, he had the other servant arrested too, against the girl's claims that she had nothing to do with it.
He guessed that it must have something to do with the eyes. No matter how much a person fabricated lies, there were just some things that their eyes couldn't hide – flickers of emotion that revealed what they didn't want to share.