It's not really blood, but it is juice from a blood orange. That's close enough, right?
A lot of people would prefer that tools and other objects used in a scene such as this one should be in pristine condition. I prefer displaying the reality of everyday life by intentionally using whatever I've been able to find around the house, whether the item is brand new and unused as in the case of my pasta ladle or is a well-worn knife such as in this scene. I was fortunate to be able to light the knife so all of the manufacturing lines and scratches going in other directions stand out so nicely.
EDIT: I added a second photo to the thread.
Setup
The tabletop is bare wood. The background is the unlit area of the room. (I think this is the first time my lighting setup didn't light the nearby wall in my tiny makeshift studio.) Two medium continuous-light lamps light the scene from the left and right sides at a 45-degree angle. A small continuous-light lamp laying on the tabletop lights the scene from the left rear to brighten the tabletop. Ironically, it's reflector also casts a nice shadow on the middle area of the tabletop.
The largest purple area on the evenly grooved part of the knife is a reflection of the foreground slice; it is not juice. The juice on the other parts of the knife is mixed with glycerine to make it thicker. The simulated droplet of juice is Aqua Gel, which holds its shape long enough to capture the image before the droplet falls off the knife. I wish I could tell you that I planned for that droplet to include the nice reflection of the orange's skin, but I'm most definitely not that good.