Factual error: In a number of episodes people are shown eating and drinking in the laboratories. For instance, in "Miss Willows' Regrets" Nick and Greg are seen eating fried chicken in the lab, and in "Overload" Sara eats a sandwich while watching Grissom experiment with her deli pickle. There are other examples. No reputable laboratory (which this is supposed to be) would allow its staff to eat or drink while in the lab. It is basic scientific protocol to prevent contamination of samples or the person picking up toxins on their food.
Deliberate mistake: Every time the investigators deal with IP-addresses, the addresses on display are impossible. Each of the four parts of an IP-address has to be between 0 and 255. As they do have to use IP-addresses some time, they could use addresses starting with 10. Those would be real addresses although not used as an official IP-address. This isn't the same as phone numbers using 555 - any IP address over 255 just wouldn't work. It would be like mentioning a phone number which uses the symbol for pi.
Plot hole: Lizzie had the car towed to icebox canyon. When you see her watching the car being lowered onto Sara, there is no tow truck there, there is no sound of any machinery lowering the car, and when the shot pans back there is nothing there that would have helped her move the car. She is not strong enough to hold up a car, put an unconscious person under it while holding it up, and then lower it without some kind of winch.
Factual error: The CSI doesn't prioritize cases by importance, and have samples from big cases go first like they do on the show. They don't have the lab in house like on the show. It's too expensive. They have to send samples from even the most important cases, to labs where it takes weeks to months to test DNA to keep down costs. They also have to do this to make sure DNA testing is done correctly. DNA has to be tested multiple times because mistakes can be made.
Suggested correction: This entry is half correct and half incorrect. It is true that DNA is not as accurate as the show depicts and no lab would run it one time. However, some CSIs do have a lab "in house" as in some units that's their "office" so to speak. Not true of all of them, but is for some. While law enforcement won't openly admit this; they do put a rush sometimes on high profile cases as they have a reputation to maintain and it won't look good to the public if results aren't coming back quick enough.
Revealing mistake: Throughout varied episodes you can see the cadavers breathe while on the examining table.
Continuity mistake: When Holly is first in Grissom's office and says that she feels light headed, Grissom offers her a chocolate-covered grasshopper and takes one for himself. Holly asks, "Is there a grasshopper in there?" and Grissom's right hand is near his waist. When the shot changes, Grissom merely smiles and eats the grasshopper, but his hand started off much closer to his chin without there being an opportunity for him to move it.
Cool Change - S1-E2
Revealing mistake: The male corpse's eye is fluttering as his arm is examined. (00:10:30)
Cool Change - S1-E2
Deliberate mistake: Willows collects fingernail scrapings from Holly's left hand in the morgue for DNA matching to Holly's shooter. In the flashback, Holly uses her right hand to scratch her assailant while her left-hand remains gloved. (00:32:47 - 00:36:22)
Cool Change - S1-E2
Visible crew/equipment: When Nicky is dragging her ex-boyfriend across the hotel room floor you can see green screens outside of the balcony doors and windows. (00:39:45)
Cool Change - S1-E2
Factual error: There are some majors problems with the "jumper's" crime scene. The girlfriend bashes the boyfriend on the back of his head. He bleeds out all over the balcony (she cleans up the blood with towels) but the body leaves absolutely no blood behind on the carpet (It's white\off white so blood would stain badly). She drags his body across the carpet and carpet fibers get stuck in his watchband by the adjustment knob. Dragging a body across the carpet would snag fibers on the opposite side. The CSI crew experiment and conclude the boyfriend was pushed. The blow to the head killed him instantly (coroner's report): therefore, the girlfriend would have dumped the body. Dumping a dead body over a rail would provide a different trajectory than pushing a live person and would not have matched their experiments. Finally, the boyfriend is fairly muscular and heavy. The girlfriend is petite. It would be an extremely difficult task to stand a lifeless body up at the balcony rail and flip him over. (If she could have lifted him up and over the rail, she should have been able to carry him to the balcony instead of dragging him.)
Cool Change - S1-E2
Plot hole: Grissom examines the victim's body and immediately rules it a homicide because he was wearing eyeglasses. He states that suicide is a cowardly act and no coward wants to see their death and would have removed their glasses before committing suicide. What a completely unfounded, and unscientific, statement. Suicide being an act of cowardice is his opinion and not a scientific fact and they don't work off opinions: they always state how they work off the evidence.
Suggested correction: This is correct, that was not scientific on Grissom's part, however this wouldn't be the last time Grissom formed an unscientific opinion that he was sure of based off what he thinks to he true as have the rest of the CSIs in several cases throughout the series. This also happens in real life; people involved in crime scenes making assumptions thus making errors off it. It wasn't right; but I would hardly call this a plot hole as this is something Grissom legitimately believes.
Cool Change - S1-E2
Revealing mistake: Dead Hotel guy's torso moves slightly up and down during his autopsy.
Revealing mistake: While the morgue's examiner opens Johnson's right eye with his fingers, the "corpse's" eyelid twitches repeatedly. (00:12:30)
Revealing mistake: The woman in the trash bin blinks as the flash light is shine on her after the team retrieved her from the bin. (00:07:03)
Audio problem: When Gil is talking to the drug dealer in the desert, he refers to him as a 'dumb punk'. But this has been dubbed over as what he actually called the dealer was a 'dumb prick' which you can tell by Gil's lip movements. (00:23:50)
Who Are You? - S1-E6
Deliberate mistake: A plumber is looking for a leak under the floor of a house, and sees the bones of a hand sticking out of the concrete wall at the side of the house. The concrete is flat, this is because in construction boards are put up and the concrete is poured in, so how were the fingers sticking out of the boards during construction? In reality, the fingers would be inside the concrete, the workman would see nothing, no plot for CSI.
Blood Drops - S1-E7
Visible crew/equipment: Near the start there is a visible mic boom just above Grissom's head to the left for a second. (00:03:23)
Blood Drops - S1-E7
Factual error: The show falls into the Hollywood myth on polygraphs. Jesse is given a polygraph test after pleading guilty to the 4 murders. He answers all questions, except the last one, honestly. The 4 traces on the polygraph show no real movement on these questions. On the final question, Jesse lies and all 4 traces spike. If polygraphs actually did that, they would be admissible in court. But the reality is, it is the opinion of a highly trained operator that decides if there is a lie. The average person could not look at a polygraph results and point out a lie. There is no huge, visible spike. The producers could have replaced the 4 traces with a red\green light: Green is an honest answer and red a lie.
Blood Drops - S1-E7
Continuity mistake: At the end, when Tina is shown the photos of Brenda they are in a pile of three. The camera cuts to a long shot and there are two in a row. Cut back to Tina and they are a pile of three again. This happens on and off throughout the scene.
Blood Drops - S1-E7
Continuity mistake: Sara takes pictures of Brenda with an UV light camera. The camera used to film the episode for broadcast is barely able to show the walls in the background as tiled. When the UV pictures of Brenda are used in the interrogation, the photos show Brenda's back up against the tile wall.