Sylas calmly watched Nosphaleen's reaction.
Normally, it would be foolish for him to do something like this. However, he had his reasons.
First, he hadn't given up on Nosphaleen. It was just that he would need a far stronger Taboo Bond Talent in order to truly turn her into a Serpentes.
Second, she might not be aware of the full situation just yet. Although she was certainly smart enough to realize that Sylas didn't lord over her any longer, there were several reasons she couldn't.
She had been unconscious when the contract was formed, and then she spent the rest of the time in hibernation, so she had no personal experience with the contracted state.