Bob demonstrates and explains.
The Goddess's Hands (or in French, La Main de Deesse) is a concept introduced in the second arc of the anime set in Paris.
Edward explains that while Solar Hands/Solar Gauntlets are impressive in Japan, first class artisans in France always have these abilities.
But the warmth they provide is not enough to knead soft breads like the Brioche. A soft feminine grip is required, flexibility that only comes to those who have trained since childhood.
Even Sophie, an expert baker and a woman, only possesses this ability in a limited sense. All three of the Kayser brothers possess it in full. Everyone is surprised to learn that both Kazuma and Kai also possess this ability (though they did not know it was named) and duplicate the finger contortions easily.
Kyo tries to hide that he is even worse off than Sophie and has normal hand flexibility.
The Kayser brothers Edward and Bob later reflect that they think Kazuma's hands are superior to their own.
The strongest Goddess hands apparently belong to Gran though, who trains a combination of extreme strength and delicacy by walking around on them.