Deliberate "mistake": Series 4 Episode 13 Silencer. When they are trying to find out who the blogger is, they back trace to the IP address the person is using, the IP address they find starts with 310, the highest number any octet of an IP address can be is 255.

Plot hole: Episode 419, "Driven". Delko pulls over Hayden early in the episode and questions him. Later on the shooter from the spa is found dead and he has glove markings on his arm. Delko tells Calleigh to compare the markings to the gloves he took off Hayden and they are a match. But Delko pulled Hayden over hours before he killed the shooter. If Delko had the glove in custody, how could Hayden have worn it during the killing?

Continuity: When Heratio and Delko are on the dock talking to the blond about "Diablo" on the close up shots you can see that there is a large yacht parked at the dock she is sitting on. When the camera switches to the shots from behind looking over the pool with her at the far end, the yacht is gone.

Continuity: Right at the beginning of the funeral ceremony, we see the prisoner exit the police car and he asks the officer to remove his handcuffs to go pay his last respects, in which the officer replies that he cannot do that. Only a second or two later, the prisoner can now be seen walking toward the coffin (not knowing there was a shooter hiding inside) and he suddenly is no longer handcuffed.

Plot hole: There is a large amount of blood found at Rachel Turner's apartment and it's determined to be Horatio's. He is subsequently arrested. Why wouldn't he be checked for a cut? To bleed that much would require a large cut and since it was only 24 hours it wouldn't have had time to heal, therefore proving that the blood although his had to be planted. That's too large an oversight by the police to just be a character mistake.

Factual error: Delko would not be able to work on the case, since he was present at the robbery and thus an eyewitness. An eyewitness who fired his gun at that. He would have been dismissed from the case.

Continuity: In Episode 4-12 "THE SCORE" When Frank is standing over the body of Paul Sanders and Alex is checking him out, as he talks to Heratio he has something on his right cheek that looks like a large pimple or covered bump. In the next scene when he is interviewing Heather Larkin in the police station there is nothing on his cheek.

Revealing: Season 4, episode 21: "Dead Air". At the start, when Horatio looks at the call details, it very clearly reads "no sim card inserted" at the top of the screen. Quite hard for the accidental recipient of the call to have a working phone without a sim card...