[EVERYTHING] - Any one else catch this mistake?

So back in Episode 2 on the boat the Sand Snakes are arguing about who gets to kill who and all. I think the youngest one says "I get the mountain" and I didn't really think anything of that last week. This week however, when Ellaria is being taken into the Throne Room there was a definite look of shock when she saw Ser Gregor alive and guarding Cercei. As far as she knew The Mountain died along with Oberyn in S4 so reminded me to last week why the Sand Snake would believe he was alive. Minor nitpicking I know but just something I noticed!