Normally, Leon would not have cared if someone was trying to tear down his faith in something or judge his actions, but in this case, Claire was hitting right on the mark and Leon's shattered beliefs and his whole future outlook were both still a little too fresh on thinly wound string of what was left of his calm.
When she turned her back on him after threatening to end him and his sire, Leon's temper snapped. He slammed his hands against the bars with a feral snarl, his fangs flashing in an instinct to threaten her back. Leon's anger had been quick and fiery since he'd been turned, all the centered focus he'd found through his magic now stripped from his mind. Added to it was the hunger that would not listen to reason. Leon was a newly turned vampire and he was in the dungeons behind a locked door for a very good reason.
"Claire!" he shouted, her final threat, that she would break her word now, ringing through him. It meant, if the staff didn't know already, that Andrei would be more at risk of being sent away. It would be just like her, Leon thought, to injure him in really the only way she could, and that was getting Andrei removed from his side. Andrei was all Leon had left. He was his family. "Don't you dare!" Leon snarled, slamming his hands into the bars again and gripping them tight, jerking hard. They rattled and rang, but they didn't give way. They were meant to hold even stronger creatures than vampires and his attempts to get through the bars to get at her were in vain.