He gives a start when Heiji looks like he's about to fall, even shifting a bit as if he were going to try to grab him before he could topple. Though from his current position, he probably wouldn't have been able to make it even if he'd made the attempt...

However, once Heiji's clearly safe, he settles back into place, looking away again.

"No. It's the room. Calhoun makes you play truth or dare. When I asked for another truth, he dared me to stab someone instead."

And he actually did it. And he hates himself for how easily he had given in. Maybe it would have been better to turn that knife on Calhoun after all - at least he would have gone down fighting instead of acting the coward.