井口

井 = 二 + 丿 + 丨 : Joan of Arc (ji) is digging a well (井) inside the engine ((e)ng3). At first she was doing it by hand, but then she hooked up a capacitor (二) to a banana (丿) and a dinosaur bone (丨), which dig for her using the electrical energy.

Mnemonic symbol: 口 shall be represented by a mandarin. Karl Marx (k-) is enjoying a mandarin in the outhouse's living room (ou3).