I'm gonna to agree with Ness on this. There's nothing like having your hands on some girl's lower ribs and feeling her squirm around. Well I'm sure there is, but you get the point.
But for the point of the discussion, if you could have some way to measure biofeedback, such as a computer keeping track of blood pressure, breathing, and other vitals, you could program it appropriately to change as certain thresholds are attained. It also would tell which areas get the most response. You'd would have to put some randomizing routine into the program so it wouldn't get predictable. So when anyone feels like putting a couple Mill into a tickling machine let me know.