Bite marks and other manifestations of teeth impressions approach fingerprints in their value as evidence, since no two sets of teeth wear the same way. A cast can be created from a bit mark to produce a replica of the suspect's mouth. If the suspect is in custody, a similar replica can be made of his/her teeth to determine if there is a match between bite marks at the crime scene and the teeth of the suspect. Teeth analyses can also reveal age, sex, and often occupation (a carpenter may show ridges from biting on nails). The development of evidence from fingerprints has been greatly aided by the use of a laser beam that creates luminescence from the riboflavin and pyridoxin transferred from the skin. Fingerprints can thus be exposed on materials previously immune to fingerprint detection. Advances in blood analysis have made it possible to identify owners of blood samples with a certainty that approaches that of fingerprint matching, and the owners of other body fluids can be identified as well, since other body fluids tend to contain major blood group substances. Analysis of the patterns of blood stains has also become a science that can reveal what happened at a crime scene. In the area of toxicology, the gas chromatograph and the mass spectrometer, working in tandem, can analyze more than 30,000 separate chemicals and then yield a reading that is virtually indisputable.