This a simple prank. It makes you look like you are bleeding under a long-sleve shirt.

Step 1: What You Need

For this you will need the following:
Some Karo (depending on how much blood.
Red food coloring (you dont need a alot)
a little bit of water
some tape
and a snack bag
OPTIONAL:
A long sleve shirt if you put it on your arm

Step 2: Mix

Mix the Karo and the coloring togather in the bag.

Step 3: Finish

Once you have mixed it all together tape the bag where you would like it. Cover it up with something like clotheing. Now just cut it with something sharp and start moving arounrnd so the blood starts comeing out.