Yesterday my two neighbors and I rented a core aerator. That time of year. It rained all day Friday (finally!), so the lawn was wet. I waited until 11:00am and gave it a cut. This takes me about an hour with the push mower, and though a core (my back yard is very steep), it is some of the only regular exercise I get so I still do it.
If you've ever worked with a core aerator you know these things are a beast. I think they were actually based on some sort of medevil torture device. The thing weighs a ton and horses you around while it tears up your yard.
I was on one of the tiers we have in the back yard and the darn thing started swinging around like it was going to go over the edge. I horsed it back hard, managing to ram a bolt on the handle directly into my left knee cap. This action prevent the aerator from going over the edge - but sent me over the edge instead. Only a four foot drop at that point, but I landed on the ankle - and then the knee - of the same leg.
Sore as heck the rest of the day, and the darn thing throbbed all night long, but I'm okay. Just reinforced though that I am getting old...
