In this video we make a fake blood cut using the classical reaction of ferric chloride and potassium thiocyanate.
Get half a gram of ferric chloride and half a gram of potassium thiocyanate. Add about 10 mL of water to both and shake them up until they are both fully dissolved.
Now get some of the clear potassium thiocyanate solution and rub it across one hand.
With the ferric chloride solution soak in it a fake weapon like a pair of scissors. Once it's wet draw it across the hand that was soaked in potassium thiocyanate. You'll get a dark red compound that looks like blood. It's a great way to scare people that you've cut yourself. What's happening is the thiocyanate is reacting with the iron to form iron thiocyanate that has a deep red color.