Arnold's stomach is the third part of his digestive system, and a field trip location in the episodes "For Lunch" and "Goes Cellular".
History[]
For Lunch[]
The bus parachutes safely into Arnold's stomach, with Ms. Frizzle thanking the class for flying "Digestion Airways". Carlos jokes about them belly flopping into the acid. The class laughs at his joke as the bus opens a sail with Arnold's face humorously printed on it. As Ms. Frizzle sails in the acid, she sings about sailing in a stomach of "slop". Ralphie notices the "pink cliffs of Arnold", with Tim correcting him that it's the stomach wall.
The class sees the gum Arnold swallowed, comparing it to Plymouth Rock. The waves in the acid become turbulent, and the bus is briefly stuck on the gum before breaking free. Dorothy Ann gives a presentation on stomach acid. The bus approaches a hole in the stomach, causing Keesha to feel bad for Arnold. Ms. Frizzle explains that it's actually a valve that leads to his small intestine. The bus lowers its Arnold sail and transforms into a submarine, getting sucked into the valve.
On the way back up, the class cycles back into Arnold's stomach from his small intestine. As they wonder how they're going to escape from his body, Wanda has an idea. The bus turns into a speaker, and she starts talking to him from his stomach. She tricks him into thinking that she's his conscious and convinces him that he's thirsty. She tells him to drink her seltzer, which he does. The bus is promptly encased in a gas bubble, flying back into his esophagus.