Only a few years ago did I notice that Darth Vader’s helmet wobbles in the wind while he delivers the “search your feelings” line (and the rest of the scene until Luke falls) in ESB.
It’s become for me one of those; once you’ve seen it you can’t unsee it moments.
Or the bit where Luke leaps down from the Carbon Freezing platform and bounces off a little trampoline…(I didn’t spot that one, I read it somewhere)!