There's an important lesson here...
If someone ever tells you that a guy has "iron feet" it is best to not get into a contest of blows with 'em...because he might really have feet made of iron and then go ahead and kick a hole in your chest on his turn. I learned that from this movie.
I love that scene actually. One of my favorite in kungfu history. It's classic. That strong man was saying, "You should be ashamed of yourself with your pathetic blows." And the mentally crippled guy was trying to warn him: "An Chu has iron feet." But the strong guy is like, "Iron feet, Iron fists. These names I know most of the time...they mean nothing." And then suddenly, it was all over.
My drill sergeant used to threaten us with sticking his foot way up in our chests when we messed up. I wonder if this is what he had in mind. Scary.