Depending on the red color you chose (always 100% saturated) the blood will look different. And the way you change the size of the brush along the way also changes it. Play with it! It's very simple!
To make a cut, for example, you have to make straight lines, as shown below 
The multiplier mode will make the inside of the line get darker as you paint over it again and again, making it look "deep", like a cut. |