What inspired the D&D version of the Rakshasa?

Rakshasa have been part of D&D for more than 35 years, appearing in every edition. These evil magic cat-people are clearly inspired by the rakshas from Hindu and Buddhist mythologies, but they have elements which indicate another source as well: so far as I can tell, backwards hands are not part of the original rakshasa concept.

  • Is there any knowledge of where this bit of backwards-hands/feet lore came from and why it was tacked on? I’ve found similar traits in creatures from many different cultures, but nothing that indicates to me one of them is more likely to be the actual inspiration (nearly all of them have backwards hands and feet, for instance).

I’m quite aware that often the answer to “why did D&D do this?” is “Gygax just did it,” or just a baffled shrug. But given the number of interviews and living information available, I’d like to get something more concrete. So although speculation may be all that’s available, I’m holding out hope for some “origin of” D&D magazine article or a similar source that draws a non-speculative line of influence from inspiration to monster.

[Context: I want to use creatures inspired by D&D rakshasa in non-D&D RPGs, and it’s important to me that I go to sources rather than simply plagiarizing D&D’s ideas.]