I had wanted to do this for some time, and finally found the perfect opportunity. After mixing up the blood, I spread the scene over the kitchen and waited for 45 minutes, until my friend David got home. I was nervous, and was having a hard time controlling my breathing and heart rate, so the prank wasn't perfect, but he was definitely freaked out. He was a good sport, though, and a great subject.
The knife was real, the blood was 1/2 water-based hair gel, 1/4 red food coloring, and 1/4 chocolate syrup. I also microwaved it to body temperature and mixed it with about 3/4 an ounce of stage blood. In total, I only used about three ounces or less of mixture, and spread it around with latex gloves. Music is "Hunter" from 30 Seconds To Mars.