I think it was McKenna who said he believes that because people hear about elves before their trips, they experience them and the experience is fairly similar. Even the name, an elf, is suggestive of the appearance of the creatures.
No one, to my knowledge, talked about "DMT elves" before McKenna. The people who talked about them afterwards were very likely directly or indirectly primed by him to expect to see them, and we all know that expectations can strongly influence what one experiences on psychedelics.
