Have you ever had a dance with a hoverfly ?
I found a great way to practise quick fire manual focus. I was stood (camera hand held) a few feet away from him, fully zoomed in with a 300mm lens, iris fully open. He would hold position for a couple of seconds then move sideways or up or down by a few inches right out of shot so I had to be quick. We danced around for 10 minutes, Some times as soon as I pointed the lens at him he would move so I then had to re-locate him try and find focus then snap him.
Although this shot isn't perfect I found it really was good practise for getting quick focus to catch pets or children and other fast moving objects.
Next time I'll remember to press the video record button.