Metaphors and analogies

I like to use metaphor and analogy when helping my students understand foreign computer concepts. I talk about traffic jams when we're all trying to look at the same website at the same time; I compare the computer to a baby, in that "it is not as smart as you are, and it may not always understand what you want it to do, but you still have to be kind and gentle to it"; I compare learning to touch-type to learning to walk (hard at first, and slower than crawling, but then so easy you don't even have to think about it); and the internet is like the biggest library you can imagine, except it lives in all the computers of the world instead of in a building, and there is no librarian to organize everything and keep bad stuff out (though there are search engines to help you find stuff), and anyone is allowed to put their own writing and recordings and movies in it, for example.

The tricky concept I'm struggling to find an analogy for now is saving, when you are saving something that has been saved before, but has had changes made to it. Misunderstanding this concept can be disastrous. For example, kids who forget about the undo command (how could they?!) are likely to think "Ok, I just accidentally deleted all of my words. I know, I'll save, and then they'll be saved, right?" Alas, no. I try to explain that the save command saves whatever your document looks like right now, and replaces the previously saved version that was there a second ago, but many are not getting it, and either I need to make a Common-Craft type of video to illustrate this concept, or I need an analogy, and I'm not coming up with one.

It occurs to me now that the best solution would be to have students (the ones who get it) make that video illustrating the concept, but I'm still open to suggestions for analogies.