Aziraphale is simply passing through the plaza, minding his own business, when he hears Death's voice and freezes on the spot. Just like that, his wings on the astral plane tuck in tightly, as if he is trying to make himself as small as possible.

Why on Earth (or anywhere) would an immortal being fear Death? Well, the last time Aziraphale saw Death, it was right before he and Crowley were kidnapped by their superiors and nearly executed for treason. Bit of a bad luck, that was. So it is with great trepidation that he looks over at Death, hoping history won't repeat itself.

...huh. Back to riding a horse again. A very much alive-looking horse. That's new.

"Er..." Come on, Aziraphale, get it together. "Hello. You're in a place called the Nexus. I'm not familiar with The Disc... did you not mean to come here?"

Please let the answer to that be yes.