His decision to keep his mouth shut helped him ride through the pain without giving Szayel any more satisfaction. Luppi grit his teeth and tried to ignore it. Ignoring the implication that he was nothing more than a dog was the hardest thing of all.

It wasn't worth it now, when every time he tried to rip into Szayel verbally could be met by Szayel ripping him apart quite literally. His glare didn't change, but he didn't say a word. He would show him what a naughty mutt he could be some other time. That was a promise that could keep Luppi going through whatever else he was left for him to endure in this lab.