It's almost always my left side. For many years I have theorized that the relatively large number of injuries that occur on my left side compared to my right must have something to do with my lazy left eye. I don't see things coming like I should, and therefore objects of many sizes have found their way to my left side more often than my clear-visioned dominant side. Consider this: My left knee was the one that got rearranged by a failed attempt to launch myself into low geosynchronous orbit. My left side was the one that merged with a Volvo station wagon when I was trying to cross the street after selling concessions at a University of Colorado football game. Both experiences resulted in brief hospital stays.
I've got a scar on my left eyebrow, my left ring finger, and my left forearm. I see a vast left-wing conspiracy forming here. Saturday morning I started in demolishing our front fence in preparation for the new and improved front fence that would be erected in its place. I heard the little voice in the back of my head that sounded a lot like my father saying, "You really ought to take care of those nails sticking up out all over the place." I heard that voice as I stepped squarely on an exposed and slightly rusty splinter. It easily slipped through the protective covering of my Converse tennis shoe and into the arch of my left foot. It came back out just as quickly as I hobbled into the house for a bandage. I considered a trip to the emergency room, then reconsidered when I saw the size and location of the wound.
I cleaned it, applied antibacterial ointment, wrapped it, and went back to work. It was during this time that I tried to recall the symptoms of tetanus. In case you were curious: Common symptoms are muscle spasms in the jaw (hence the common name lockjaw), followed by difficulty swallowing and general muscle stiffness in other parts of the body. Then I stopped thinking about it and finished the job.
Yesterday, my wife did the right thing and got me an appointment with our physician. He looked at the hole in my foot and deemed it less than serious, but said it was a good thing that I came in to have it checked out. Then he ordered up a DPT, a mixture of three vaccines, to immunize against diphtheria, pertussis, and tetanus. This keeps me safe from myself for the next ten years, or as long as my common sense holds out. When the nurse returned with the syringe, she swabbed me up and jabbed me - you got it - in my left shoulder.