If Johnny were calm and rational at this point, he might notice Topher takes no particular joy in this. No smugness or anything, nothing to indicate he's proud of himself for manufacturing an impressive bit of illusion and trickery. That's Gabe's business.

Even if Johnny doesn't believe him, doesn't want to believe him, hopefully it'll plant enough doubt that Johnny tries to look more critically at Gabriel. Try to see him for what he really is.

"That's what I thought, too," he answers grimly. "Got me nowhere good."

He does notice what Johnny's doing to the floor. He's particularly aware of any changes made to the dreamscape, even after that little trip down memory lane.