I read part of an Alfred Hitchcock a long time ago. It was about a guy who would see movement out of the corner of his eye, but when he looked, there was nothing there. It turned out he was seeing creatures - their name started with "P". What is the name of this story?
A story matching that description can be found in the anthology, “Alfred Hitchcock Presents: My Favorites in Suspense” (1959, Random House).
The story is called “They bite”, by Anthony Boucher (originally published 1943).
Set in the desert of California, “They Bite”’s Carkers lurk around the town of Oasis, hidden, hungry, snatching what they can. Boucher builds a legend up around them with a few cultural references and a few dangerously imprecise descripives: “something moved, something little and thin and brown as the earth. Too large for a rabbit, much too small for a man”, and, “something like a man and something like a lizard, and something like the things that flit across the corner of the eye”, and,“something very dry and thin and brown, only when you look around it isn’t there. Ever see it?”, and, “you glimpse lean, dry things out of the corner of your eye… take the Carkers and the things you don’t quite see and you put ’em together. And they bite.”