As Rancid Rabbit imprisons the citizens of Nearberg for not having a license for whatever species they are, he finally makes it to Mr. Sunshine at whom he pauses for a while, trying to figure out what he is exactly. Finally he simply states he's under arrest for not having a license.
As the duo set fort in their room awaiting the arrival of the horror monster, Toothpick Head, they watch as a plethora of other horror movie monsters appear in their room doing generally silly things (eliciting no reaction from the duo besides a laugh from Dog).
And the toothpicks? There's hundreds and thousands, and... millions of them...
"I HAVE CHOCOLATE"
The educational tape:
"Thinking is fun! It makes the brain happy!" "Hi, Happy Brain!"
"You...you did this to me, bow-wow person! You made the smarts go bye-bye!"
When Cat first starts losing his brains, he tries to get smart again by watching one of Dog's educational videos. Except...he doesn't know how to fit a tape in a VCR anymore, and ends up smashing it to bits.
The episode "Party Animal", especially the roller coaster scene.
In The Great Parent Mystery, Lube heads to the Parents Day celebration with parrots, mistaking it for Parrots Day. Rancid corrected him, and Lube's parrots fly up with Lube afterwards.
In "A Dog Ate My Homework," anything with President Rancid is hilarious, but this moment is the funniest: while waiting for Dog to come and eat his speech, Rancid starts to read it. The crowd boos him, and he tries to edit the speech. This doesn't work, so he starts singing "Tea for Two" and dancing to an ever-increasing chorus of boos. There is also this comment after it happens:
Random Senator #1: This is the most embarrassing thing I've ever seen the President do!
Some of the jokes in the background are chuckle-worthy, such as a tour bus saying "Willie Nelson Medicare Tour" in "Hotel CatDog."
In "Nine Lives", the shot showing the angry mob, which includes the Greaser Dogs covered in cement with a mouse probably moved them, Mr. Sunshine and his cow, and a personification of Earth is quite hilarious despite being in a dark scene in the episode.
In "Hotel CatDog" we see the exterior of the house-converted hotel in the night and several vehicles parked. The vehicles even includes an airplane and ship.