The 4/3/13 episode of CSI: Crime Scene Investigation titled "Sheltered" begins with the idea of a potential animal bite in the victim's leg. Even though this did not turn out to be the case, animal activity is often something that must be considered in crime scenes. Someone who has died inside their residence, even of natural causes, and not found for a considerable time period may display damage due to pet activity feasting on the food source at the house.
Oddly enough, it is thought that dogs hold out for a longer time period than do cats. I have cats and sometimes their facial expressions seem to be saying "don't tempt us". But that's another story.
Meanwhile, outside animal activity may include the scattering of tissues and bones for several feet/yards away from the body. Hair and clothing pieces from the body can be located in nearby nests of birds and/or rodents. Shiny objects like buttons, jewelry, and cartridge casings are attractive to animals and may also be carried away to nesting places or dens.
The other interests in this episode revolve around chemistry. The crane origami paper was treated with ninhydrin. This reacts to the amino acids left within the remnants of the fingerprints within the porous paper and produces a purple coloring. I would also like to note how proud I was to see Fin photograph each stage of the unfolding of the crane. This procedure should be followed when anything needs to be unfolded, be it a towel, a bed sheet, or an origami crane.
Then they probably used luminol to locate the presence of blood. Luminol reacts with blood and creates a chemiluminescent reaction. Think of the glow of a firefly's butt. In simple terms the same kind of reaction. The thing about luminol is that it is usually used when only traces or non-visible blood needs to be located. If you can visually see the blood stains there is really no need to utilize luminol.
It should also be noted that the reaction is sensitive but not specific in reference to blood. This means that it will react and "glow" with a reaction to a mere drop or two of blood in a bathtub full of water (sensitivity) but can react to things other than blood (specificity) like metals or vegetation.
The last chemical test that I'd like to talk about is that used for the detection for the presence of blood. This is a screening tool and is only used as an 'indication' that blood is present. Phenolphthalin is added to a swab which has been used to collect a test sample. Hydrogen peroxide is then added to the swab and a pink color is considered a positive reaction. If heme in blood is present, the O2 in the hydrogen peroxide will use is peroxidase-like activity to break down the H2O2 into H2O (water) and O2 (oxygen). The O2 oxidizes the Phenolphthain to Phenolphthalein which is pink.
Now that you have had a dose of Chemistry 101, I must go. My cats are giving me that eye look that says I should be giving them attention or they won't wait that extra day or two upon my demise......