One cow contains approximately eight gallons of blood. When cows are magically turned from things that smell bad into things that taste good, all of that blood generally goes to waste. But it need not be wasted, for it can now be used to make large structures and waterproof bricks that also happen to look kinda like fresh-baked brownies. Mmm, brownies.
Animal blood, specifically cow blood, is "one of the most prolific waste materials in the world," according to a recent U.K. architecture school grad by the name of Jack Munro. Munro decided to try and figure out whether cow blood could be used for anything architecture-y. After experimenting with making glue, he found that by mixing in some sand (and a preservative), and then baking that for one hour at just 160 °F, you can make waterproof and structurally passable bricks. Of blood.
Essentially, using blood to make blood bricks takes the place of using mud (and water) to make mud bricks, making the process potentially ideal for arid climates where you have a lot of cows and a lot of sand, but not a lot of water to spare. Beyond bricks, and glue, it also may be possible to make much larger structures by covering entire sand dunes with blood, letting it dry, poking holes in it, and then waiting for the dune to migrate with the wind, leaving a giant hollow shell. Of blood.
You can see conceptual pictures of some of these giant blood dune structures, as well as some real pictures of testing that Munro has done with real blood, in the following gallery. Of blood.