Karo syrup, when mixed properly, makes extremely realistic fake blood when shot on video. In a large bowl, mix 1 cup of Karo syrup and 1 tbsp. of water. Use a wire whip and mix until it reaches a desired consistency. Add 2 tbsp. of red food coloring and continue to whip it until the mix is a dark red color. Add 1 tbsp. of yellow food coloring to lighten the blood for best effects on video. Experiment with more yellow food coloring to change the shade of the blood.
This recipe produces movie blood that is not edible and harmful to the eyes as well. Add alcohol-free hair gel to a bowl. Use 3/4 the amount of gel as the blood you want. Add a small amount of automobile transmission fluid and mix until it turns watery. Mix in half the amount of "super strength" red food coloring as there is liquid. Add some chocolate syrup to make the water more brownish. The mix will be thicker than water and flow like real blood.
Smooth peanut butter is easier to use but chunky peanut butter makes great, coagulated effects for zombie movies. Mix the peanut butter with corn syrup in a large bowl until the blood reaches the desired consistency. Slowly add drops of red food coloring until the mixture is a dark red. Make sure it is a dark color because bright red blood looks fake on video. Since the blood is edible, this is a perfect concoction to use if you need blood to spurt out of your mouth.