is it really how someone who just won looks like?
I think the first gif is far more telling than the second one.
It’s a sudden moment of sheer panic. For their whole lives, Thor has been this immovable, invincible mountain. He’s never been hurt or anything, and Loki finds comfort in that because it’s something stable and unchanging. Thor is Thor, he won’t change. He won’t leave, he won’t turn against him in anger.
But now, none of that holds true anymore. Loki has just sentenced his brother to death (with the half-certain knowledge that Thor will escape) and the consequences of that have abruptly broadsided him. Thor is not invincible anymore. Thor is not standing beside him, laughing at one of Loki’s pranks. Thor is plummeting 30,000 feet straight down towards Midgard’s surface in a cage that Loki trapped him in.
Suddenly, all those games and sparring matches they had as young men have melted away in the face of this new battle they’re fighting. Suddenly, everything is terrifyingly and viscerally real. No more games. No more tricks. They’re equals (opposites), now, and Loki is going to prove it, whatever the cost.
And Loki can’t help wondering: “what if I’m wrong? what if he doesn’t come back?” Because out of everything, that would be the worst nightmare of all.