While Seth might have simply looked like he was staring down this depraved youngster as he yapped and whined about his pathetic, stalker life. But the moment that he started to yell and spit his words at being called 'Human', Seth knew he was a lost cause.
If he wanted to play the villain, then he could have his little monologue. Why would Seth interrupt him when it gave him ample time to prepare? And prepare he did.
He couldn't cast his threads from his puppets, not unless he was possessing them, and with this creepy teeny bopper eagerly telling him, in a round about way, that he was able to take the powers of others, there was no way Seth was going to risk his soul by possessing Corvus.
All he would need to do is heed some caution when it came to certain attacks, such as blue fire. He was not making that mistake again, especially with the risk that this creep could have eaten the heart of a similar Raven.
