Oh man, you reminded me of one of my favorite Youtube classics, the Windows Vista speach recognition: https://www.youtube.com/watch?v=KyLqUf4cdwc
Alternatively, it could be some kind of sound that's not common to English. In fact, your could make up a whole command structure based on sound "gestures". It would sound funny, but the ease of use would trump those awkward verbal commands. The sounds could mimic natural sounds for mnemonic ease.
It could be made to sound _hilarious_! :-)