1.First, you can see that Jake has emails from Det. D. Goor, Sgt. M. Schur, and Det D. Miner — Dan Goor, Michael Schur, and David Miner are all executive producers on Brooklyn Nine-Nine.
2.In the episode "HalloVeen," you can spot a cute photo of Amy and Jake on Amy's desk — the picture is actually taken from Melissa Fumero's Instagram.
3.When Charles and Jake write their "No-No List" while on a stakeout, Jake writes that Charles is a jerk, so Charles puts "no jerks" on Jake's side of the list.
4.On the wall in the break room, "Stop stealing Terry's yogurt" is written on the chalkboard.
5.In the precinct, you can spot a "Safety First" sign that reads: "Always keep the gun pointed in direction of face," "Always keep your finger on the trigger and ready to shoot," and "Always keep the gun loaded and ready for use."
6.When the gang is forced to work the night shift, the name plates on their desks have been changed, since different people work during the day.
7.When Trevor's dad comes to pick him up after Jake arrests him for tagging police cars, you can see that Trevor drew a butt on Jake's computer.
8.One of the flyers hanging in the precinct during Season 1 advertises a community center dance show called "Floorgasm."
9.Terry's portrait of Capt. Holt can be seen hanging in Kevin's office at Columbia University.
10.Capt. Holt has a plaque commemorating his service on 9/11 hanging in his office.
11.Gina reveals that after Amy has had four drinks, she's more likely to have sex. Later, when Jake and Amy go on their first date, they both order four shots and end up sleeping together for the first time.
12.After Gina tells the gang that they are actually drinking cement, everyone stops drinking except for Scully.
13.Jake and Charles have matching police figurines on their desks — TBH, Charles probably bought them.
14.While in the witness protection program in Florida, Holt keeps his lawn in pristine condition, while Jake’s lawn is a mess.
15.In the background of this scene, you can see that Hitchcock and Scully have created a system to pass papers to each other without getting up.
16.When Capt. Stentley arrives, we learn that he can't work the blinds. Later in the episode, you can see that the blinds to his office aren’t closed properly.
17.And after Capt. Stentley leaves, you can see that he left his bongos behind in Capt. Holt's office.
18.On the wall in the conference room, you can spot Scully's detective award from the Association of Polygraph Examiners.
19.In Capt. Holt's office, his binders are arranged to display the colors of the pride flag — the binders are later placed in the same order behind Gina.
20.In Season 4, Capt. Holt mentions that there are two acceptable sleeping positions — in Season 5, you can see him executing one of them.
21.You can spot an old photo where Capt. Holt is standing next to Kevin while all of the other couples are embracing — Holt has talked about how tough it was being a gay police officer.
22.In the first Halloween heist episode, you can see that Capt. Holt keeps his sandwich in his safe.
23.On Gina's desk, you can see she has a jar that reads, "Ashes of Problem Employees."
24.After Vivian breaks up with Boyle, he knows it's officially over when she gives him his dehydrator back — Gina does the same thing after she and Boyle stop sleeping together.
25.And finally, during the first Halloween episode, Amy spots a Raggedy Ann drinking vodka straight from the bottle — in Parks and Rec, Ann is dressed as Raggedy Ann and drinks vodka from the bottle.