He didn't know how the registrar was doing the marking. He couldn't even see any moving parts at it worked.
The registrar was a simple metallic box. Yet, it was doing something to him without him seeing how. He could only wait patiently for it to finish what it was doing.
It didn't take long for him to be marked. When he was done, the robot said to him, "Please, step beyond the registrar."
He pushed the wall beyond him and felt his hand sink into it.
This was strange and interesting, but it didn't shock him because he had read about it in the military codex. He knew what to do, which was to continue pushing forward.
He did so and continued to do so even when his entire body sank into the metallic wall. With one last push, he sank completely into it.