It could be anything physical. But i think the Hip to Waist
ratio plays an important part...especially for the 1st
impression...then comes other things like the eyes, the lips, the
legs, mayb for some..even the hair...but i dun think its just one
item that makes her attractive...its the combination..her overall
presentation that will determine her sexual presence...being touchy
may help... 
but over do it... and it may become a turn off...
well... To Each His Own!! 