The reason is just part of the lesson. They both know that the gifts will hurt differently. But when this real thing is properly trained, it will bed for pleasure and punishment both. It will seek out sensations, the line too blurred to make out arbitrary judgments. It will lose its perspective about everything that doesn't involve being a good Thing that does what it's told.

"Good pet. You may have it now."

He passes over the mirror, giving Cisco a glimpse into the real side. The perspective is of the center of a table facing up, but there's the occasional flash of motion. There's a sharp object, and a scuffle. Blood splatters into the mirror, obscuring Cisco's view. If he focuses long enough to tune into thw sound, there's only screaming.