Lisa's poem contains two equations:
(eq. 1) 4 paws + 1 tail + 9 lives = 1 special cat
(eq. 2) 1 special cat - 9 lives = 1 sad little girl
...........1 special cat = 1 sad little girl + 9 lives
Or, transitively, 4 paws + 1 tail + 9 lives = 1 sad little girl + 9 lives
Subtracting 9 lives from each side means: 4 paws + 1 tail = 1 sad little girl
During Homer's final fight with the Killhammad Aiee, right after Homer makes the first shot to the robot's "groin", it picks him up and begins to shake the fake robot shell around him. When the shot shows the inside of the hollowed out robot during this, if you look just above Homer's left arm on the right side of the frame, Maggie bounces up from the floor and is clearly visible for a moment. At no point in the episode is Maggie ever seen entering or exiting the robot, so this odd little "Cameo" goes completely unexplained, as Homer doesn't seem all too worried for her safety when the robot is destroyed moments later.
This is the second episode featuring robots that are programmed to harm other robots but not humans. The first was Itchy & Scratchy Land.
Homer is seen wearing a welder's mask during his ill-fated attempt to build a robot implying that he must have acquired one after nearly burning his eyes out in The Fat and the Furriest.
At Snowball II's funeral, Marge makes an attempt to cheer up Lisa by saying that according to Lisa's religion, Snowball could have been reincarnated. However, this is an incorrect statement. In Buddhism, there is no eternal soul that's reborn in another body. All that remains is a person's karma, which is passed on to a new person upon their birth. While Marge's statement can be overlooked as her lacking knowledge about Buddhism, Lisa doesn't correct her.
When the crazy cat lady throws Lisa a cat, it has a red collar, then moments later, the collar disappears.
The announcer says that only men want to see the Robot Rumble but there are women in the audience.
Homer popped out of the robot even though the robot was made out of metal, it is unclear what Frink's robot was able to do with Homer, or the metal.
Homer has his injuries cured, but, it was only about 3-5 days after that.