Brooklyn Nine Nine is a show that perfectly balances serious crimes and character reveals with some legitimately laugh at loud antics - which it's managed to pull off from its first episode all the way to its current seventh season (with the eight incoming).
This constant blend of comedy and drama means that you're usually pretty deeply engrossed in either the episode's jokes or its ongoing mystery, meaning that it's really, really easy to not spot things. This is doubly true when you learn that the production team involved in making Brooklyn Nine Nine seemingly constantly hid small details, gags, and nods to earlier episodes everywhere they possibly can.
The result of this is that when you inevitably binge-watch the show for the fourth or fifth time (we've all been there), you notice a bunch of new stuff in episodes you've already seen before. Indeed, this sort of gives you an excuse to watch these seasons again and again, because you'll always find some extra moments you don't remember seeing.
Also, sometimes you learn a little more about one of your favourite characters, and that's worth its weight in gold. Or in a Halloween trophy - either or.
10. Terry Skipping With His Twins
One of the best things about Brooklyn Nine Nine is that the characters within it are fully fleshed out, with storylines and character developments so nuanced that it's clear they were planned seasons beforehand.
This is evident from the pilot episode. While we learn here in dialogue that Terry has twins, you also get a glimpse of the golden-hearted father's parenting style, as we can see him skyping with his girls halfway through the episode.
The show never hesitates to show Terry as a good father - whether he's painstakingly building his kids a toy castle that takes hours to be put together, or making sure his job as a police officer doesn't come before his role as a dad. While it's clear Terrence was going to be a good parent from the start, it's wild to think that his whole shtick with puppets was laid out episodes before we even see his kids whatsoever.
It's a well-known fact that Sergeant Jeffords is a man who cares, but the full extent is something that is shown just as much in backgrounds as it is in the main plots of the show.