ציטירנדיקער פּירוש אויף שמות 34:8

מפתח האהל, he began running from the entrance of his tent. When a person is observed to perform any task with speed, with keenness, this reflects that he considers what he is about to do as important. We have another example of such conduct in Exodus 34,8 וימהר משה ויקוד ארצה וישתחו, “Moses hastened to bow down and to prostrate himself.”

כי קרן עור פניו THAT THE SKIN OF HIS FACE BEAMED — קרן is an expression connected with the word קרנים “horns”, and the phrase, קרן אור, the light-“horned” , is used here because light radiates from a point and projects Like a horn. And whence was Moses privileged to have the rays of glory? Our Rabbis said that they originated at the time when he was in the cave, for the Holy One, blessed be He, then put His hand upon his face, as it is said, (Exodus 33:22) “And I will shelter thee with My hand” (Midrash Tanchuma, Ki Tisa 37).

נקוד, I believe that this describes these spots in the region of the neck and head, as the word ויקוד means bending down with one’s head and neck. (Exodus 34,8) The word ויקוד has a dagesh in the letter ק, as on that occasion Moses’ bowing down was equivalent to his prostrating himself, i.e. more than just bowing down. The word is of the category of נפל, which in a similar construction would also be ויפול with the dagesh inn the letter פ. The קדקד is the head, but is also connected to the foot, as the line ויעקוד את יצחק means that he bound Yitzchok’s feet. (Genesis 22,9).