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Sara Sidle's sudden departure from CSI shortly after she accepted a proposal from Grissom and transferred to another shift so they could be together without jeopardizing their careers - especially since her reasons for leaving (specifically, "ghosts" from her past cropping up since the death of her father) fly in the face of why she hooked up with Grissom (he was a stabilizing point in her life who, for two seasons, helped her greatly).
Also from CSI, Sara's inability to practice basic survival techniques in the season 8 premiere, even after years as a CSI when she should have either gotten a brief lecture as a part of bonus job training or learned the basics after she encountered someone who died while hiking in the wilderness, like the guy Grissom found while searching for Sara.
Well she did have the idea of carrying a reflective surface (a car's side-view mirror) around, which did help in eventually finding her...
How about CSI's "Fur and Loathing"? Behind Wall Banger Number One: Latex lining for a Fursuit! Yes, latex, which traps heat and moisture in an already extremely warm costume. He'd cook in that thing. Even without latex, everyone in a fursuit (which most con-goers wouldn't be, given that they're expensive and not every furry wants one) would be cooking... even without having sex or making speeches under hot lights. Did the furry con take place in a giant walk-in freezer?
CSI has a tendency to induce this trope on a particular subculture when they do an episode about them. The furry episode is simply one of the best-known.
Season 5's "Committed": the murder is captured based on a confession he made in a pottery class; the sound was captured in the grooves of a pot like a vinyl record. They hook the pot up to a laser beam to play the conversation, and they can hear it perfectly. How many laws of physics does that recording defy?
Sounds more like something from "The Roads Not Taken" from Fringe.
Technically it doesn't break any laws of physics and the clay would hold some sound, just not enough to be clear no matter what was done to analyze it.
In one episode a guy gets electrocuted because the murderer pushed a nail through his rubber sole. During the explanation why this is bad they tell us that you are safe from lightning in your car because the tires are made from rubber, which keeps you insulated. Let's hope that nobody believed them.
Rubber-soled shoes do protect you from electrocution, to an extent. They're federally mandated in certain industries because of this.
The part no one should believe is that it's the tires keep you safe from lightning in your car. In fact you'd be just as safe from lightning if the tires were gone and the wheel rims were sitting on the ground. An arc that jumps several hundred feet isn't going to stop because of a few more inches between ground and car. What keeps you pretty much, though not perfectly, safe from lightning in a car is that the car's metal body forms an equipotential shell, or Faraday cage, around you. See this great clip from Top Gear.
Speaking of CSI video game episodes, CSI: Miami 's "Urban Hellraisers" episode is incredibly stupid. From the guy playing himself to death to the entirely wrong portrayal of video games to the game company having people commit crimes from the game for advertising: stupidity after stupidity for an hour straight.
Oh, but don't forget the female perp's reason for joining in: "[Gamer guys] won't even talk to you unless you're a gamer!" You are encouraged to reread that as many times as you have to before it starts making sense. Plan ahead for bathroom breaks.
Another one from CSI: using silica as GPS Evidence. You know, the second most common molecule on the planet. It's quartz dust, people!
From CSI: New York, the episode centered around Second Life. Sure, the episode had about every inaccurate gaming trope (despite help from the game's developers); but the real Wall Banger was when the perp got away. First of all, she was so desperate to get away that she shot an innocent bystander and then leaped down a garbage chute. Yet, in the shot between those, we see her walking calmly down a flight of stairs at a clipped stride because she's in six-inch heels. Wouldn't she have yanked her footwear off to go faster? Despite that hobbled pace, she still manages to outrun the police, who didn't take that long to see that the bystander was safe. Bad Video Game portrayals in a videogame episode is one thing; the final chase following slasher flick physics is something else.
Another one from that episode — the chase scene that happens in Second Life. If you don't want to talk to someone online, log out, or, better yet, don't respond. Why did he direct his avatar to run, and why did the police chase after him?
Another monumental one from New York: in the Season 6 episode "Redemptio", Hawkes is trapped in a prison while his nemesis, Shane Casey, is about to escape while disguised as a cop. Mac, from the safety of NYPD HQ, warns him that SWAT will storm the place in 10 minutes. Hawkes himself has help in another inmate who armed himself with a drain pipe. When the latter catches up to Casey, he tackles him and the two wrestle their way out to the courtyard, where the SWAT sees a policeman assailed by an inmate. Then said inmate takes out the pipe (which he should've attacked Casey with in the first place) and is shot dead by the force. Hawkes comes running out a few moments later, dressed in a convict's uniform, but instead of submitting immediately to SWAT and stating his identity so he has some credibility, he immediately starts ranting and raving about "That man is not an officer!" while Casey walks away happily and escapes. Oh, and the rest of the CSI team? Not only did they ALL stay at headquarters, not one of them had the foresight to tell the SWAT captain that Hawkes was dressed as an inmate, which they all knew at the time. (At least they can be excused for not telling SWAT that Casey was impersonating an officer, because Hawkes himself never told them even when he had his phone in hand.)
On CSI: New York, an escaped convict's master plan for escaping to Canada is to hijack an airliner in New York City and fly it to an abandoned airstrip near Montreal. The plan has several small flaws: first, Canada, being half of the NORAD system, would know immediately a hijacked airliner was heading north. Second, as Canada has police as well, said airliner would be surrounded when it landed. Third, the escaped criminal could have quietly taken a train or a bus to upstate New York and walked across the border a few hundred meters away from any border crossing post, with no one the wiser.
Another CSI: New York one was Aiden's departure. She had to have wanted to quit or be fired, because it doesn't take much intelligence to know that you don't leave the empty evidence bag in the box where the boss is sure to find it.
Aiden's death got many fans as well-they were pleased she wasn't killed when she was written out, then annoyed she was brought Back from the Dead.