By Rachel Ehrenberg Web edition : Tuesday, March 1st, 2011

 Text Size CHICAGO — Some crime scenes are exactly the size of a breadbox.   Every year forensic scientist Brendan Nytes sees a few cases where a dead rat or mouse is found in box of cereal, a jug of vinegar or a loaf of marble rye. His job is to distinguish genuine contamination from the surprising number of cases involving the intentional introduction of a dead rodent to a perfectly wholesome food product. While critters do make their way into food accidentally, many arrive with outside help, said Nytes, a microscopist with Microtrace, a private forensic lab based in Elgin, Ill. A careful postmortem may lead investigators to a litigious consumer, vengeful employee or maybe just a kid with a sick sense of humor. When a product containing a dead animal arrives at the lab, Nytes reported February 26 at the annual meeting of the American Academy of Forensic Sciences, he and his colleagues first scrutinize the crime scene. Gnaw marks on the inside or outside of the container may reveal a point of entry or an attempt to escape. Feces or urine within the container can indicate whether the animal arrived in its tomb alive. But the autopsy is often the most revealing part of the investigation, and may quickly rule out death by food processing. Ligature marks on the neck?  Probably died in a mousetrap. Analyzing stomach contents can reveal the green dye used to mark rat poison or an empty stomach, both questionable if the rodent died in a box of food. “Emaciation is unlikely if it died with an unlimited food supply,” said Nytes. As any CSI fan knows, establishing cause of death is much easier with an intact corpse. When faced with a few bones or scrap of fur, scientists must first ascertain what animal they are dealing with. Some body parts allow for a much quicker ID than others, said forensic morphologist Bonnie Yates of the National Fish and Wildlife Forensics Laboratory in Ashland, Ore.  “Teeth are great because that’s how animals make their living,” said Yates. Tail or rib bones, not so much. “But if you have a remnant of original form, chances are if you have someone who knows their way around a carcass, they will know what it is.” Occasionally there isn’t a carcass at all. Nytes has seen cases where package contents really settled during shipping — so much that a consumer misidentifies a misshapen mass of oats and starch as a body part. “This is actually a big deal — a consumer often claims it’s a rodent, and it isn’t,” said Nytes. “It’s a rock of product.”