Knowing what it felt like, Harrison was prepared for adverse reactions. The blood could have an obscene, profound effect on body and mind. A single drop felt like life essence itself. A mouthful was unlike anything else in the world, like everything had been turned to full volume, full intensity. But he knew just how difficult it was stop. He'd clung to Zoom's arm more than once. Even after fighting and trashing against it. Even after all Zoom had put him through, he could not force his fingers to loosen.

But as he watched Barry, even without a grip on his arm, he could tell something wasn't right. He couldn't place it. He'd only ever experienced it from the inside before, but his gut told him this was wrong. Even if he couldn't put his finger on exactly what it was, at his very core he knew this wasn't normal. Not for a human, and not for a speedster.

"That's enough," he said. His hand planted on Barry's shoulder for stability and support as he pulled his wrist away.