- This episode proves part of Castle's hypothesis about why Kate became a cop (1x01) correct. In particular, it illustrates perfectly the statement that she's wounded (her dogged pursuit of the answer even after they find the culprit), but not that wounded (she chooses to tell Castle her story, he doesn't drag it out of her.)
- Beckett keeps her watch (seen since the pilot), her badge, and a ring she wears on a chain under her clothes (seen for the first time here, but implied to have always been there) in a memory box with her parents' picture on it. It looks like the box also has a drawer in which she keeps her weapon.
- Beckett wears her weapon in a holster at the small of her back.
- According to the epguide on IMDB, Scott Paulin appears uncredited as Kate's father in the picture on the memory box (and apparently in archival footage that was never shown). Paulin will finally appear as Beckett's father, Jim, in 2x13.
- Castle is a speed reader.
- As far as marriage goes, Castle 'loves the institution, hates the day-to-day.'
- Alexis is very used to her father asking her questions about bizarre ways to murder people. Also, part of the plot of the Nikki Heat book appears to include incinerating a body in a self-cleaning oven.
- Once again, Alexis provides an essential clue which cracks the crime.
- Castle guesses that one of Beckett's parents was murdered, but he assumes it's her father because she wears a man's watch. The watch, she later tells him, is indeed her father's but it was her mother who was killed. She and her father were waiting for her mother at a restaurant. They waited two hours, then went home to find the police already there, a Detective Raglan. Presumably, her mother's body had been found by then (otherwise the police would not have been waiting for them) but we don't know exactly when she was murdered (or, at this point, how many years ago). The detectives called it random gang violence and it was never solved.
- Beckett's father became an alcoholic afterwards, but has now been sober for five years.
- Beckett wears the watch for "the life that I saved" and the ring for "the life that I lost". The latter is clear, but not so much the meaning of the former. Possibly Kate had something to do with getting her father into rehab/therapy for his alcoholism and this is what she meant by saving his life.
- Castle says that "Night" is boring, and "Until tomorrow" is more hopeful, to which Beckett replies "Yeah, well, I'm a cop. Night." In her roundabout way, what Kate seems to be telling Castle at the end is that she herself does not believe in hope.
- Esposito gives Castle the file, but it's unlikely he expected Castle to remove it from the precinct.
- Kate's mother's name was Johanna.
- Not really an oops, but a public service announcement for TPTB: women DO take off their makeup before they go to bed. Particularly when sleeping alone. And if they do not, it does not look pristine perfect when they wake up.
- It's amusing how Kate's team seems to be the only one handling homicides in all of New York (and by extension, Lanie appears to be the city's only ME.) IRL, they would not be woken up for a fresh body at 5am -- the graveyard shift would have caught it. Likewise, the bullpen would not empty out at night like a regular office.
- Despite railing at cops who put cases in boxes which leaves them unsolved, Beckett puts Sam's case in a box herself, dismissing the fact that the cop who investigated Melanie's disappearance didn't have the neighbor down as a witness. Were it not for Castle forcing the issue, they would never have found out that Melanie's dad killed Sam.
- Waiting over a day before reporting someone missing isn't exactly an admission of guilt - generally you can't file a police report before someone has been missing 24 hours, unless there are special circumstances (ie it's a kid, or there are suspicious circs). Granted, most people at least call the police before that, even if they can't file an official report, but still...