When concentrated 30 % or 100 vol. hydrogen peroxide, a strong oxidising agent (CORROSIVE use protective glasses and gloves when handling) comes into contact with some left-over blood from a heart or pluck dissection demonstration, a fantastic reaction takes place forming what looks like a strawberry sundae.
The hydrogen peroxide is unstable and decomposes into oxygen gas and water at a slow rate. When added to the blood the enzyme present called catalase speeds up this decomposition creating massive amounts of oxygen gas very quickly which are trapped as bubbles forming a foam.
It's use as a desinfectant for cuts and wounds is somewhat debatable and it's not really proven to be beneficial in any way except to remove dirt and debris from the area surrounding the wound.
For more information and excellent infographics have a look at the Compound Interest website: