Factual error: The plot is about a mosquito who stung the murderer. Although Gary Sinise mentions (correctly) that only female mosquitoes bite, the one caught alive on the table is a male mosquito (look at its bushy antennae and abdomen which is thin and definitely deflated). All mosquitoes used in the episode are male.
Factual error: when Mac Taylor's ID card from the Marine Corps is being shown, there are two unintentional mistakes and one probably intentional. First, the design of the ID card in no way resembles an actual DoD issued military ID, but this was probably an intentional mistake by the creators of the show. The picture on the ID however, has two unintentional mistakes. First, Marines are never photographed in their dress blues for official purposes; Mac would have been in cammies or service dress charlies for the photograph. Second, Mac is revealed in several episodes to have been an officer, yet he is shown wearing the dress blues of an enlisted man.
Factual error: When they are looking at footage of the suspect leaving the crime scene they notice something in his sleeve and the computer generates an image of a steering wheel lock. There is no way they could come up with that from the outline in the suspect's clothes.
Continuity mistake: Mac is crouched down on the ground and removes a piece of paper from the grass next to the victim without a crime scene glove. He has a flashlight in the other hand with no glove either. The next shot shows him standing with gloves on both hands.
Other mistake: Hawks is handed a pretty small container with some of the victims brains in it, and says there is about 50% of the brain still left out there to find. There is no way half of a brain is in that small container, it's not even filled all the way.