Lawn Mower?!

Lawn Mower?

Dad was up early Saturday morning mowing with a gas lawn mower around some trees near our pond. The grass was still wet from the dew, which made the slope he was mowing very slick. While lifting an evergreen branch, Dad’s foot slipped under the mower!
He was very lucky, the blade didn’t cut through his shoes. It did whack his big toe a few times before he managed to pull his foot out though.
A few days later, Dad was telling the story to a neighbor, and showing him his bruised and swollen toe. The neighbor took a close look at the toe and then said, “Looks like you need to sharpen your lawn mower blade.”

I might be being a little backward, but I dont think I understand that!