Cesar kept ripping off his own flesh, the pain was so intense that tears started streaming down his face while being drowned with his blood. With a deranged expression, desperate to see the end of his madness, he continued eating his own flesh, destroying the arms he had once carefully cared for.
But if his right was thinking, the arms he had was superficial.
Even so, it is real.
Superficial is different from fake after all.
These superficial emotions, the surroundings, and everything he was experiencing... Cesar thought everything originated from somewhere... somewhere within himself.
If he was right, Cesar knew he had been attacked through his mind.
The powerful mental attack probably came from the Nightmare, and Cesar can pinpoint that it's the ability to manipulate the darkness that Jeremiah 'superficially' dismissed in the image he was seeing.
It was 'superficially' arranged by the Nightmare.