http://www.steamykitchen.com/75-baking-the-perfect-loaf-of-french-bread.html
Now do a little “karate chop” lengthwise down the middle of the bread and stretch out the long ends again. Fold over in half. The karate chop helps get the middle tucked inside.
I didn't understand this "karate chop" thing. What exactly does it expect me to do after I fold the sides of the dough?