Factual error: When Castle and Beckett go to talk to the victim's assistant, there is a chalk outline on the floor where the body was discovered. Although it's common in police dramas, chalk outlines are not actually police procedure, because it contaminates the crime scene. (00:08:40)
Revealing mistake: When Castle arrives at the murder scene and views the victim's body, the "corpse's" eyelids are twitching.
Answer: The networks are now having winter breaks. A mid season end of new episodes, when they come back after the new year, it picks up as if several months have gone by. Beckett suggested Valentine's Day as a "chick flick" to watch as she is moved in. Also some episodes are not scheduled to air in order.