Me, in a steady tone and tempo which sounds like I know where the missile is, or am updating listeners on the opening times of a Dog Park: "Do not be concerned if you hear a Sound. The Sound will be very loud. Following the Sound you may hear the shattering of porcelain, or see water flowing freely from under the door. The Sound is not itself an indication of distress; further, less iconic sounds will follow in the event of possible physical disaster."
Mrs Fox: "...did you just tell me you're going to the bathroom?"
Me, smiling pleasantly: "I'm going to use one of those fizzy tablets and scrub the thing."
Mrs Fox, tired: "why the fuck are you like this"
The tablet knows where it fizz at all times. It knows this because it knows where it fizzn't. By subtracting where it fizz from where it fizzn't, or where it fizzn't from where it fizz (whichever fizz greater), it obtains a difference, or deviation. The guidance subsystem uses deviations to generate corrective commands to drive the tablet from a position where it fizz to a position where it fizzn't, and arriving at a position where it wasn't, it now fizz. Consequently, the position where it fizz, fizz now the position that it wasn't, and it follows that the position that it was, fizz now the position that it fizzn't.
