This is irrefutable because I say so, and because I say so, it is irrefutable.
At the same time it is very probable, and indeed it has often been known to happen, that witches do actually and indeed suck children's blood, which they draw either by some sharp needle or by the scratch of their long nails, or else by the aid of the Devil they pierce some vital vein, and scars are left by the tenderest parts of the child's body, whence they have sucked the hot life-blood, and the child becomes anaemic, wastes away, and dies. This cannot be gainsaid since it is proven by irrefragable testimony, and it has been demonstrated that after witches in the form of cats have been seen to attack children, blood is noticed to trickle and trill from wounds, although they may be very small, and accordingly the Devil hath been busy here.
--Montague Summers, The Werewolf in Lore and Legend, 1933.
Yes, he's serious.
I now know why Cthulhu investigators lose SAN over reading mythos tomes.