I am one of the worst canine agility handlers on the face of the planet. Agility is basically an obstacle course for dogs. The human handler gets to walk the course, which is different every time, and plan how to get the dog through in the shortest amount of time possible. I trip over obstacles, forget what they're called, wind up on the wrong side of things, run into my dog, wind up off course, you name it, I've probably done it! I'm working on my skills, especially since my collie puppy Havana has the potential to be a great little agility dog, but it is slow going.
One of the things I've been told - over and over and over again - is to call out the next obstacle as early as possible. Then the dog doesn't have to switch gears from "run full out mode" to "what's the handler want? mode" or worse "well, I'll just figure it out for myself mode". When I manage to give my dog fair warning, we run our course very well. At least until I run into something. When I don't get obstacle names out, I wind up with a dog who either decides to do his own thing (Cousteau) or I get a thorough barking at (Havana).
This has made me think of BabyBug. When she plays, she plays very intensely. Many times she moves from one thing to another so quickly that it's fairly easy to catch her and direct her to what needs to be done without a problem, but not always. I find that if I pick her up without warning when she is absorbed in something - like watching the dog eat or scribbling on the grocery list - there will be a tantrum and I usually end up getting kicked or almost dropping Bug as she does her "I've got no bones" protest.
I read in some child rearing book or another about giving the child a warning that play is going to be ending so they can start to shift gears. It is different from agility in that you are giving a cue ahead of time to shift gears rather than to continue on in the activity, but the end result is the same - a smoother transition. I've been making a point of telling Bug as soon as possible "we need to see Daddy soon" or "in a minute we need to get your coat". She has no concept of time, but she hears "Daddy" or "coat" and she starts to think about what that entails. Even something as simple as saying to her "Can Mama have that?" if I need to take something away from her, rather than just taking it, seems to be enough transition to keep from a tantrum. Usually.