yeah dundee openly admits about putting his thumb in the glove hole, making it even bigger and stalling to give clay more time to clear his head. henry's hammer was a hell of a left hook. he was left handed aswell which is probably the main reason it was so affective.
dunno about how the cut came about but dundee certainly had a few tricks up his sleaves. but cassius clay was still undeveloped and young when he faught cooper.