My favorite reaction of a ticklee is one with a giggly girlish squeal laugh, and toes which flex back away from me when the foot is being tickled. I've heard some girls say that they basically wiggle their toes wildly if their bare soles are tickled, but in my experience, the toes of a girl being tickled on her bare soles usually tend to move just one way according to the individual girl.
Ive noticed that some girls will always flex their toes back away from the tickler when tickled on their bare soles, while others will point the toes downward. I think my favorite way for the toes to move when tickled is to flex, as I feel it allows better access to the toes while tickling the foot, and allows the ler to get underneath the toes better. In my experience, girls who point their toes downward when tickled make it tough for the ler to really explore the whole foot or tickle her under her toes, cause the foot is all scrunched up. Maybe this is just me, but this has been my experience. I'd be curious to hear what others experiences have been.