The Miracle of Fountain Pens

Jasmine: *plays with fountain pen* Wow! That's so cool! Where does the ink come from?!?
Cheng: It's a fountain pen, it works on capillary action.
Jasmine: *looks at pen from various angles* Oh, there must be a switch somewhere

Note: this was happening during a lecture and despite the tranquilising effects of the lecturer, I assure you, Jasmine was indeed sober at the time.