I believe in most North American dialects "corn" is one of the only open "o" in common usage. Try to pronounce an "o" without ending it in a "w" sound. Just hol

I believe in most North American dialects "corn" is one of the only open "o" in common usage. Try to pronounce an "o" without ending it in a "w" sound. Just holding it longer... and then stop without closing your lips.