Heard of it, then. A guess based on...what. Something that shouldn't exist? Seems to be, from her reaction.

A grain of truth in every story. As they say. It leaves little for any of them to work with. His knowledge of curses runs deep, but it's predicated upon how they function in his sphere. He isn't sure that applies entirely to Dean.

"He knew almost nothing else," he says. "Only that this curse links him to a unique blade."

Geralt believes him. It's an incredibly Dean fucking thing to do, to take a deal and worry about the consequences afterwards. But the brand exists without the blade here, in this world, so the magic must be held by something else. Something more. Curses as a general rule are not inherently complex. Not in application. It is the cost of removing one which makes them so dangerous.

And some curses cannot be removed until it has run its full course.