Just what it sounds like.
How do architects celebrate Halloween?
By building things out of blood.
Seriously, though. J.S. Munro, a 2012 graduate of London's University of Westminster, is transforming one of the world's waste materials into a construction tool: cow blood and sand into bricks. There's plenty more information on his construction techniques on his website.
His final project, Sanguis et Pulvis, for a brick-making factory in the Egyptian desert, won him first prize in university. That project involves casting the blood-brick material over a sand dune and letting the sand drift away, creating a sheltered space beneath. The technique, he thinks, would be particularly useful in desert climates where water is in short supply.