Bloodshot eyes
I just watched this film I think for the first time since I was a kid. When I'd seen it in the past, I think it was on black-and-white tvs (yeah, that long ago), so it was a treat to actually be able to see Dracula's bloodshot eyes. I remember reading a mention of the film in a book on movie makeup and special effects when I was a kid, in which it was stated that Lee wore special contact lenses to achieve the bloodshot eyes effect. I wondered what the hell that had looked like, since I had never been able to see it.
Nowadays, an effect like that can even been done with CGI, but it was pretty cool seeing it just using oldstyle contact lenses.