Whisk together the cocoa powder and cornstarch.
Whisk in the water, followed by the red gel, purple gel, and corn syrup.
Add any more color if necessary. To make it thicker, add a little bit of cornstarch or cocoa powder.To make it more opaque, add more cornstarch.Too thick, add a little bit of water. The fake edible blood should be smooth in texture and have the viscosity of melted chocolate used for a drip cake, or a royal icing glaze.