Gender: Female Location: in a double decker bus...
The LETHIFOLD
In re-reading all the HP books in preparation for HBP I came across an entry in 'Fantastic Beasts and Where To Find Them' I had seen after I read OotP the first time but then forgotten about. In the British edition, it is on p. 25 of 'Fantastic Beasts'
LETHIFOLD (Also known as Living Shroud):
The Lethifold is a mercifully rare creature found solely in tropical climates. It resembles a black cloak perhaps half an inch thick (thicker if it has recently killed and digested a victim) which glides along the ground at night.
...the Patronus is the only spell known to repel a Lethifold... Once its prey has been successfully suffocated, it then digests its food there and then... leaving no trace of ... its victim behind.
((the dots are because I have omitted bits of the text that were really long/unecessary))
I think that this is far too big a coincidence for JK - surely that entry is there as a hint of what killed Sirius!
A lethifold glides along the ground. Not hanging. And it doesn't have to draw its victims in like a siren does, it attacks sleeping people. The guy in the short story was lucky enough to wake up, grab his wand.
Anyway I doubt it. I had wondered if dementors were derived from the lethifolds but that would seem implausible since JKR said that the former grow like fungus where there is decay. The veil on the other hand was symbolic of the veil between life and death.