Is it ok to mess with your kids' minds?

I found this post from the Dibert blog amusing. My sister frequently comments when I mess with the kids. I do this all the time. And I mean more than just pretending that you've grabbed the kid's nose. (Tom likes to do that one). For example, Maree used to annoy me with her constantly asking what's for dinner? So I told her "Martian eyeballs." At first she was really grossed out. And a little worried. But she caught on fairly quickly that it's really just spaghetti and meatballs. No harm done. I can't think of any specific incidents, but I think I learned it from my Dad. I think it's generally harmless, as long as you're not mean with it and you know when to stop. There's a good chance it'll help them, it'll give them good stories to tell one day (to friends or their therapist) it encourages them to use their imaginations, and it's fun for Mommy.