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.
Character mistake: Seven minutes into the show, Sarah Sidle is about to do an internal sexual assault exam/kit on an unconscious victim in the hospital, Sarah picks up a metal speculum and says aloud to the victim (in a presumed moment of empathy), that she "never really liked this part of my yearly exam. These things are always freezing" referring to the speculum in her hands. She then brings a speculum to her mouth and begins to blow open-mouthed on it two times, forcing her hot breath on it to warm it. She then begins to insert it into the victim as the scene cuts away. This is pure stupidity, as no trained CSI would ever contaminate the tool like this. Sarah just added her own DNA to the speculum via her breath so any saliva or body fluids are now on the speculum what she is about to use on this patient, who is now also exposed to any STDs from Sarah.
Plot hole: A central plot device in this episode is that there is no six letter word made up of the letters EXVIN, so the murdered man cheats at the word game by playing a word he knew to be inadmissible - exvin, a wine connoisseur who no longer drinks. Since he is supposed to be a stone cold killer player at this word game, don't you think he would have thought of Vixen? Sara Sidle points that word out later - why wouldn't a world champion word game player have figured it out, using a safe, common word and avoiding a possible challenge?
Factual error: The murderer kills the two students by drilling a hole through the adjoining wall of the victim's room at floor level, placing 40lbs of dry ice next to the hole, and allowing the sublimating carbon dioxide to pass through the hole into the victim's room and creating a toxic atmosphere. Since the two rooms are at the same air pressure, the only possible way for the CO2 to move from one room to the next is to be pumped through. As neither room has an excessive level of carbon dioxide in the atmosphere the sublimating gas would fill both rooms until the CO2 levels in both rooms was the same.
Revealing mistake: Season 5 Episode 18 "Spark of Life": when they show a closeup of the badly-burned woman during her debridement, it can be seen that even though her eyebrows and hair and, in fact, 90% of her skin has been burned away, she still has long, full eyelashes.
Factual error: Several problems surround the electrocution death and the investigation. First, there is the insinuation that the boots should have protected the victim from the electrocution because of the rubber soles. Regular shoes and standard work boots will not protect anyone from electric shock. You are still grounded. You have to wear special electrician's boots to insulate you from electric shock. These boots cost about triple standard work boots. Second, the CSI crew found a nail embedded in the boot. They theorized that is how the boots were grounded out. The problem there is the nail had to be pushed all the way through the sole and through the insole for it to work (the close up of the boot showed the nail in all the way). Even if the nail was barely through the insole, the victim would have felt the nail poking him at every step. With the nail all the way through, he wouldn't have even walked two steps before puncturing his foot on the nail. Third, there is the nail itself. When Grissom is examining the boots trying to find why they failed (failed to prevent the electrocution), he poses the question "What is the most common item found during construction?" The answer is a nail, and the nail in the boot appears to be a roofing nail. The construction site is for a multi-story prison. Nails aren't used in the construction of multi-story urban buildings: concrete and steel are. Carpenters come in after the building is erected and work on the interior, but there are no roofing nails.
Continuity mistake: When Sara takes the photos of Lady Heather's neck bruising you see 2 distinct ligature marks. When Brass serves her with the search warrant you can see only the remnants of one ligature mark, then when she is in Brass' office later she again has 2 ligature marks.
Plot hole: A large part of Nick's plotline revolves around the discovery that the couple's stolen ring has a fake diamond switched out for the real one. But the ring was left as collateral for a very expensive necklace for the woman to wear that night. There is no way that a jewelery store would accept a ring for collateral without appraising the ring's/stone's value first. And in that inspection, they would have discovered the switch and not accepted it.
Continuity mistake: Series 7 - Part 1: When Sara and Warrick are at the table discussing the case, Sara's box containing her veggie sandwich changes position depending on whether the camera is looking at her or Warrick. (It moves from directly in front of Sara, and then several inches to her right toward the edge of the table).
Other mistake: In episode "The Good, the Bad and the Dominatrix" When the son goes to the bank he tells the manager that there was a million dollars in that account last week, there was 843,508.00 taken out leaving a balance of 31,053.86. That only adds up to 874,561.86. Not a million dollars. He doesn't say close to a million dollars He says there was a million dollars in that account.
Factual error: Grissom and Catherine are looking through a microscope and discussing a microscopic specimen (heart of frozen body). In reality they would not see anything as all microscope objectives are missing on this instrument (the microscope nose-piece is totally empty.). (00:21:00)
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.)
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.