The Chuck Long bootleg play was perfectly executed in addition to being unexpected. First off, Harmon sold that he had the ball. He didn't make a half hearted dive into the line, he went in like a man fighting for the goal line, or at least a first down. Mike Flagg, who was option two on the play, had to hold his block long enough to not let the contain man get to the edge and force Long sideways. Chuck had to turn his back completely to the defense for what had to seem like an eternity. Finally the blocking back, either Fred Bush or Rick Bayless, had to take out the weak side linebacker, the one in best position to read the play. He did read the play but get his legs taken out just enough where he couldn't reach Long.
Flagg was open at the goal line if needed. But the play was executed so well that Long was able to walk right in, holding the ball high over his head.
Footnote: Many people believe that ended the game, like Houghtlin's final play field goal a couple weeks later would. It didn't. There were still thirty seconds left. Michigan State quickly completed a couple passes and were around Iowa's 40 yard line with a decent shot at a hail Mary (a better chance than Drew Tate vs LSU anyway). Devon Mitchell batted Bobby McAlister's final pass away in the end zone, but even then Mark Ingram almost caught the ricochet.