For those of you who watch a lot of crime shows, this segment is for you. Here are a few CSI terms that will further your knowledge of investigative techniques.

When you watch an investigator examine a crime scene on TV, he/she might pull out a substance and spray it on objects in the room. The stuff being sprayed is called luminol. It's an  illuminate chemical mixture used to detect traces of blood.

You'll probably see glowing green splotches on the ground. That's where the perpetrator, also known as perp, tried to clean up his victim's blood, but some invisible traces of it remain behind. Spraying luminol on the traces makes them visible.

A chemical reaction occurs when luminol comes into contact with hemoglobin, an oxygen-carrying protein in blood. The iron in hemoglobin causes the chemicals in luminol to react, meaning that their atoms rearrange to form new molecules.

Since the original chemical molecules had more energy than the newly created molecules, during the reaction the extra energy is disposed of in the form of light. It's the same thing that happens when fireflies glow.