The eyes have a unique shape to them, like a low and wide triangle.. The eyelids drag down on the outside of the eyes, creating a deep fold.
Never without his beard, and usually wearing a stetson hat.
I've felt for a while now that there's something weird about the way he writes. The pacing of his books, strangely, is much like in a movie and the way he writes and describes what's happening makes me feel like I'm reading a movie. No, not a movie script, but a movie. It's something that I feel really sets him apart when it comes to writing style.
Terry Pratchett, secretly a vampire
Also large, flat ears.
Here he is talking about his Alzheimer's: