I could picture something added in the shot where the saber flies toward Rey and she grabs it, and Snoke’s torso falling over. Maybe when his upper body tumbles over, a whiff of that blue smoke/flame could waft up and then disappear. I think the throne is out of focus during that moment, so it would still be subtle. I guess the idea is that a part of Palpatine’s essence was inside Snoke, controlling him.
This.