Demon!Eliot - Booth
Booth didn't invest to much in what the demon inside Eliot was saying. He knew he couldn't, it wasn't Eliot controlling the words it was something else. A demon from hell, the black eyes kept him grounded. Was a nice reminder that this thing wasn't his friend anymore. But even so he didn't want to do any damage, so he was taking it at half power. They seemed evenly matched but he really couldn't tell. He didn't want to find out either.
He knew the Latin, but he'd been so distracted by the thing infront of him that it felt like his entire body wanted to freeze. How did Sam deal with this on a daily basis? Booth couldn't imagine doing this more than once. Blocking and countering and wash, rinse, and repeat.
Starting on the Latin he watched how Eliot reacted. With the rock salt spread around the block soon it wouldn't belong before he'd get something out of him. He'd been studying it since he arrived. It helped that Seeley was an altar boy as a kid so he had Latin in his background. The language was a second for him, so it made learning the exorcism easier.