Prepare your blood. Pour clear syrup into a bowl and add red food coloring. The more food coloring you add, the darker your blood. You can add some ketchup later on for a little more texture and to help darken the mixture.
Remove the sausage casing from its plastic wrap and cut it to the length you want your intestines to be. Five to 10 feet is an adequate length. Tie one end of the casing off and secure it with a rubber band.
Add the blood mixture to your filling and mix it well before putting it in the casing. Fill the sausage casing with something pliable. Cooked spaghetti noodles, soft clay or petroleum jelly are ideal fillings because they are squishy. Reserve some of it to add after you've filled the casing.
Pack the filling into the casing as tightly as you can while leaving enough room to squeeze it around for effect when it's finished. Pour some of the extra blood mixture into the casing so you've got the effect of running blood. Twist the casing into lengths from bottom to top and secure each length with a rubber band. Each section should be about a foot in length.