Quick Historical fact: From what I understand, ancient authors referred to the "turned thumb" during the games, but without ever specifying in which direction (since, back then, it was obvious to everyone). Because of that, it's a bit tricky to figure out exactly which gesture meant what. 

Some say the thumbs down ordered a specific kind of execution, while others think it was a sign to lower weapons, with the thumb representing the sword (but there's also this thing about tucking the thumb inside the hand to say "Alright, let's stop that shit", so basically, it's a total mess). Anyway, voilà ✨

✨ Some close ups (and spoilers...?) ✨

I really wanted Geta to have his thumb turned down, since he's the one deciding who dies and who lives. I also wanted to establish a kind of connection with the blood pouring out of his glass to Caracalla's dagger. A subtle reminder of the moment Geta throws his glass content to his brother's face.

The blood on Geta's neck and the dropping blood from Caracalla's hidden ear is a reference to their fates in the movie.