Did you even read the story? He pinned the snake down and CUT ITS HEAD OFF. If he was able to pin it down and cut its head off, he could have JUST AS EASILY trapped it.
He had it pinned down.... Its not like he did a matrix jump through the air and sliced it blindfolded with a knife.
He could have easily trapped it but he chose to be a jerk about it and try to be a tough guy and cut the snakes head off.