Bart: [Bart dresses himself as a carnival barker and stands beside a wishing-well] ... Step right up, ladies and gentlemen and... Mongos! Dive, dive, dive for buried treasure! This is the exact spot where the Spanish Armada was sunk by the British Navy, leaving millions and millions of Spanish Dubloons at the bottom of the sea!
[Remember, they're in the middle of the desert, on America's Western Frontier!]
Mongo: Spanish balloons? Mongo take chance...!
[and, after suiting up]
Mongo: ... How Mongo get air?
Bart: From this wonderful antique pump. Good hunting!
[and, once Mongo climbs to the bottom of the well]
Bart: ... Time for my lunch break.
[He lowers a sign to Mongo which reads "For more air, deposit $.25"]