Varying ticklishness.

The subject could have certain areas that are more effective in tickle torture. Stuff like maybe their toes are more sensitive then their furred sole or pads? Vice versa? Their feet are so so but their pits are just too much for the to take? Just fun ways to find what spots make them squirm and plead more. Randomized spot finder. Maybe certain areas get more sensitive when other things are done/applied to them (oils, brushes, etc)