[slingnow]

Not sure that "being able to hit undo" and "no harm done!" is what makes blowing things up enjoyable, but to each his own.

[dvgrn]

Heh, well, I'm speaking as somebody who was fairly obsessed with making Rube Goldberg domino chains as a kid, spending hours at a time covering a large oak trestle table with precarious stacks of wooden blocks, rulers, tape cases, strings, marbles and so on -- and then knocking them all down. (This was long before YouTube, so I don't have any documentation of any of this.)

I would really have appreciated an "Undo" button for rewinding entropy and running those things over again, especially when they went disappointingly wrong halfway through...!