Pour light corn syrup into a mixing container, and add 1 tbsp. water per cup of corn syrup. Stir thoroughly.
Sprinkle flour (or cornstarch) into the mixture and stir until it's smooth. Continue to add flour and stir until your fake blood reaches the desired consistency.
Drip red food coloring into the mixture. Use approximately 10 drops per cup of liquid mixture; you can add more later if needed. Mix it well.
Add one drop of green food coloring and stir it together. If making large quantities of fake blood, repeatedly add one drop and stir until the red darkens.
Add 3 to 5 drops of blue food coloring per cup of fake blood. The blue provides a natural hue when mixed with the darkened red. If you wish, you can add more red or blue to experiment with color tones and find the desired shade.