Thuringwethil

[Rune Son of Bjarne]

I think the skin change is of a magical sort more than just simple disguises. I cannot say how Luthien and Beren transform into these creatures, because it is not told. But "magical" skin change is not an unknown thing. In alot of the old legends and in Norse Mythology you see this happen and are never told exactly how it is done.

In the Volsunga Sage (Vølsung Saga) Fafnir turns into a dragon after killing his brother out of greed. In other stories we are told how the god Freya posses a swan skin, wich enables her to become a swan and fly. Or how ordinary people puts on wolf skins and becomes a wolf (or werewolfs).

So I am kind of agreeing with Macalaure