This is heading towards being the same thread as “obvious things you didn’t notice about your favorite work for a long time”, but I don’t think mine was obvious.
In Indiana Jones and the Last Crusade(now 22 years old), I thought Elsa had really tried to choose the right grail for Donovan and simply been foolish about picking the fancy one.
Because I grew up seeing it that way, my wife had to be the one to point out the Elsa knew she was picking a bad one and killing Donovan. She exchanges a knowing look with Indy about what she is doing, too. I guess I just missed it growing up.
Makes way more sense for her character that she is intentionally screwing over Donovan.