BoJack Horseman is easily one of the most densely-packed shows currently on the air - literally every moment of the show is stuffed with jokes, sometimes ones so subtle you don't even realize they were there in the first place. It would take too long to go over EVERY hidden joke and reference in the show's recently-released 4th season, so we'll just go over some of the sneakier animal-based jokes and puns.
Present in both the past sequences and the modern day ones is a (hair-having) turtle, who is performing the exact same action then and now - waxing. He's a turtle....waxing his truck.
Because TURTLE WAX.
There is an incredibly quick establishing shot in episode 5 ("Thoughts and Prayers") of Mr. Peanutbutter's mansion, when a peaceful-looking llama (in Todd-inspired fashion) skates by and does a quick little ollie on his skateboard.
As Hollyhock waits at the airport gate to visit her mother, we get a quick view of the airline she's taking - a pig-themed airline called "Sow West Airlines."
Pig...airplanes....WHEN PIGS FLY.
As Todd and Emily eat at the diner, they...well let's just skip to the chase here: COW TIPPING.
In a very quick establishing shot outside of Princess Carolyn's apartment building, we see a frog desperately trying to cross the street - zigging and zagging to avoid traffic. It's just straight-up Frogger.
When Diane and Courtney Portnoy are leaving a restaurant, they're suddenly accosted by a badger who won't leave them alone (until Courtney pulls out her gun, that is). He just keeps pestering them, despite their protests.
In other words, he keeps BADGERING them.
Pretty much EVERY license plate visible on BoJack Horseman has some kind of subtle joke to it - but Princess Carolyn's is particularly great: YOL9LVS.
Instead of YOLO ("You Only Live Once"), hers stands for You Only Live 9 Lives (because of being a cat 'n all).
Here's what you need to know - Civets are small mammals indigenous to tropical regions of Asia and Africa...but the thing they're best known for is eating coffee cherries and then...pooping out the coffee beans after digesting it. At that point, the beans are harvested - as SOMETHING in the process of digestion by civets make the resulting beans taste AMAZING (and the coffee produced from these beans can be quite expensive).
Anyways, that's why the symbol of "Civet Coffee" is a cup emerging from a butt. THEY PUT THAT MUCH THOUGHT AND EFFORT INTO A TOTALLY UNNOTICED BACKGROUND JOKE.
The state seal of California is...A LITERAL SEAL.
For comparison, here is the ACTUAL California state seal - you'll notice there really is a bear at the bottom, the main difference being in BoJack Horseman, the bear cub is wearing a onesie.
BoJack Horseman likes animal references (duh), particularly whenever they can squeeze in a subtle one about horses (since it's the main character 'n all) - and while this one MIGHT be a stretch, if any show would stretch this far for a song reference, it's BoJack Horseman.
In America's "Horse With No Name," the lyrics start off with:
On the first part of the journey
I was looking at all the life
There were plants and birds and rocks and things
There was sand and hills and rings
The first thing I met was a fly with a buzz
And the sky with no clouds
We first see what's become of BoJack this season in episode 2 ("The Old Sugarman Place") - BoJack has gone on a journey of introspection (so the whole "journey" bit) far away from Hollywoo...where he wants to be nameless and anonymous (aka a "horse with no name") and the first connection he makes there is a fly (well, a dragonfly, but this feels close enough).