If you have ever put peroxide on a wound you notice how it foams up white?
Thats what it does when it contacts blood. I use it as a last resort on skimpy blood trails. It works good to find single drops of blood especially in the red/brown leaves and also in pine needles. You know how sometimes when you are trailing a wounded deer you pick up every leaf that has red spot on it just to realize its not blood? With the peroxide you just bend a bit and spray and move on. I used it to find one doe last year. Mix in some food coloring and it will foam up that color. REd and green will foam up a bright orange.
A good way to see the effect of this is to collect the bloody drippings from a pack of chicken or beef and make a blood trail in your yard.