I have a slightly different explanation:
My girlfriend is very ticklish. Not the most ticklish I've ever seen, but definately above average. I rate her ticklishness like this:
armpits: 8, Hard laughter and begging
stomach/ribs: 7, giggling and laughing
feet: 9, Hysterical laughter and extreme begging.
inner thighs: 1000, she has this spot on her inner thighs, kind of where her butt turns into her legs that is right off the ticklish scale. If I tickle her there she will instantly go into wild convulsions, fits of weird noises, and silent laughter. I can only tickle her there for about 20-30secs at a time or she would probably pass out. Its not from being out of breath, the reaction is instant. She says that the ticklish sensations she gets from this spot are in describable. She says when I hit the "right" spot she can feel the sensations through her entire body, its like every tickless nerve in her body all meet in that one spot.
It's wild!!
I've tickled other girls who I would consider more ticklish overall, but none that can match that one little spot 🙂