The Neighbor Ladies are very happy, because Big Mouth is staying with them at Viv's house for a whole week. They begin singing, but then someone "goes potty" on the rug, and Peg uses the Process of Elimination to determine that it was Big Mouth who did it. He agrees to use the bathroom, but then goes potty on the rug again. Peg explains that it's because on Big Mouth's planet, there are no toilets. The Neighbor Ladies declare that Big Mouth can't stay with them if he keeps going potty on the carpet, but they still want him around, so they hide under the couch because it's a "really big problem".
Peg agrees that it's a really big problem, but states that it can be solved with potty training. She then explains to Big Mouth that Earthlings are not born knowing where to go potty, but everyone on Earth learns, and that's what potty training is. She then gives a list of steps, in song:
1.) Listen to your body.
2.) If your body says you have to go, go to the bathroom.
3.) If nothing comes, wait.
4.) When it comes, wipe.
5.) Flush.
6.) Wash your hands.
After an explanation of exactly what "listen to your body" means, they take Big Mouth to the bathroom, but he doesn't like waiting, so they sing a song that consists of only the words "boomy" and "boom" repeatedly to keep him entertained, writing down the number of "boomy"s and "boom"s down on a piece of toilet paper.
They then try to go to the store to buy more yellow things for Big Mouth but he needs to go to the bathroom again, so they get out of the car after a bit of confusion over what order to press buttons in.
Then, they go back, but Peg realizes that she flushed the piece of toilet paper down the toilet and none of them can remember how many "boomy"s and "boom"s the song has. However, when doing the "counting backwards from five" thing, Big Mouth remembers that it is three "boomy"s and two "boom"s due to the "three, two" part. They dance out of the bathroom, then realize Big Mouth is fully potty trained and sing a song about it.
This episode provides examples of
- Aliens Speaking English: Downplayed. Big Mouth speaks English, but has a speech impediment and says some words in alien speak.
- Amazing Technicolor Wildlife: Cat is indigo.
- Amusing Alien: Big Mouth provides some comedy with his wacky behavior.
- Big Eater: Cat uses being hungry for one more piece of cheese as an example of something your body might "say".
- Chewing the Scenery: Big Mouth and the Neighbor Ladies hiding under the couch while expressing the "really big problem".
- Cloud Cuckoo Lander: Big Mouth has a preoccupation with little, yellow things.
- A Dog Named "Dog": A cat named Cat.
- Exposed Extraterrestrials: Big Mouth wears no clothes.
- Mister Strangenoun: Big Mouth's name is just two words.
- Toilet Humour: Big Mouth going potty on the rug, the Neighbor Ladies saying that Peg was a "stinky toddler" before she was potty trained.
- Toilet Training Plot: Teaching an alien who doesn't have toilets on his planet how to use one.
