This is sort of three discussions in one, but since they're so closely related I thought I'd just combine them.
During the final seconds of Mufasa's life, starting right when Scar digs his claws into Mufasa's wrists, what was running through Mufasa's mind? I would expect he realized what Scar had been up to, but do you think he knew that Scar would also drive Simba away from the Pridelands?
Also, when Scar was busy making his impression on Mufasa's final seconds, Simba was right there watching the whole thing. We know this by his horrified expression and scream as his father fell from the cliff and into the stampede below. And yet, even after seeing Scar throw Mufasa into the stampede, he never realizes that Scar was responsible until Scar himself admits it to him.
My third discussion may seem nit-picky, but would Scar really be able to throw Mufasa that far out from the cliff with the grip he had?