Any miscellaneous item lying on the lawn that gets in the way while you're mowing. After you run the item over pieces of it may attempt to "bite" you as they're spat out the sides of the mower. This item could be anything from a golf club to trash that your neighbor plucked off his lawn and threw onto yours.
Herman: Hey, have you seen Collin's leg?
George: No, why? What happened?
Herman: He ran over an extension cord while he was mowing the lawn last night. It got stuck in the mower and started whipping around, cut up his leg really bad.
George: Gotta watch out for those damn lawn sharks!