I love giving instructions to the bad students...

"No, your other right hand"... (insert foot, arm, "left" etc.)
"No, step outside of the body, or you'll run into them..."
"No, keep moving..."
"No, your other katate grip..."
"Are we leading, or following?"
"Try getting out of the way first..."
"Twist the wrist..."

... and my all time favorite... "down always works"...

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What man is a man that does not make the world a better place?... from "Kingdom of Heaven"