The Mythology & Folklore Database
One of the witches noticed him and shouted to another one, "See what a large burl that willow branch has. I'm going to drive my ax into it, so I can find it again next year." And she drove her ax into his back.
He only felt a single stab, but from that moment onward his back was very heavy, and when the sun came up he saw with terror from his shadow that he was now a hunchback.
Nevertheless, the following year when the first of May was approaching he could not restrain his desire to return to Glocker Mountain, because the dances had pleased him so much. Seated once again in the willow tree, the witch saw him, as before, and said, "I want to pull my ax out of the willow burl, so I won't lose it."
She reached for his back, and he felt a light stab. From that time onward his hump was gone. When the witch pulled her hand back, she was holding an ax.