When I was recently in Pittsburgh, giving my sister a much-needed break from taking care of our mother, I heard a sharp cracking sound, followed by something hitting the floor. I was sitting in the kitchen at the time and raced down the stairs to find my mother on the floor, beside the desk, in the den. The keyboard shelf was lying next to her, with the keyboard dangling slightly above, still attached to the computer by a cord. “Are you okay?” I asked, helping her up and into the chair. She didn’t seem to be injured. “I’m okay,” she said. “What happened?”  “I fell,” she said. “What happened to the desk?” I asked, though I already knew the answer. She must have used the keyboard shelf to help herself up from the desk chair, and it couldn’t support her weight. “I don’t know,” she said, with a sense of surprise. “Really?” “How’d that happen?” she asked. “Did Ollie do that?” I asked, referring to my 14-pound Westie, who had spent the morning downstairs with …