Somewhat impressed, Severus let up with the magic gradually and studied the other man closely for any signs of fatigue. There was no pain, which he supposed was mildly acceptable. Winchester's fortifications were not the problem - he seemed to be able to maintain them at a steady rate, but he still seemed to pause and second guess himself. "The image of your brother - did you know it wasn't him because you're aware it's of my conjuring or was there something you noticed?"
The idea was to find the cause of Winchester's skepticism and make it all the more difficult to discern. He would need to be certain of himself in the days to come and that included knowing who was real and who was not. For the time being, he seemed to be of sound mind, but the deterioration yielded likely dangers ahead.
"Think. Quickly. And be certain of your answer."
Even as he spoke, he kept a close watch on Winchester's mind, having a feeling the boy would lie to him out of a sense of self-preservation. Both brothers seemed of the sort.