What is a Red Cap?
Some of the most bloodthirsty Scottish elves are the Lowland castle spirits. They are called Red Caps . . . The Red Caps' main occupation is colouring their red caps, which they dye with human blood. They throw boulders onto travellers from their towers, then catch the blood in their caps. As soon as the blood dries and the color fades, the Red Caps look for new victims.
--- From A Field Guide to
the Little People
by Nancy Arrowsmith
So watch yourselves! Hee hee hee!