Many ways for making edible blood for cakes and cupcakes, from piping gel to corn syrup based, but this one is using chocolate!
Step 1: Ingredients and Method
Basically, this following recipe is what we called ganache.
You can use white chocolate and tint it with red gel food coloring, or you can use red chocolate wafer/chocolate coating/melting chocolate, such as from Wilton (I get mine from Bulk Barn - no brand, in Canada)
While the ratio for making proper ganache is 3:1 (3 parts chocolate to 1 part cream/heavy cream) - to cover an 8 inch round cake, but for drizzling on cake/cupcakes as blood shown on pictures, just use a handful of red chocolate wafer, melted in microwave with 30 seconds interval each time, and add cream once melted, by a tsp each to the desired consistency. Let cool slightly before drizzling it on cake/cupcake so your buttercream won't melt. You can also place the red chocolate wafer and a little cream into a bowl, heat and stir.
If you are using white chocolate, tint the cream with red gel food coloring first before adding into chocolate.