Let me set the scene for you: I've just finished a major cleaning and organizing sprint in the main living area. A slightly cheesy "greatest hits" classical music CD is blasting something along the lines of The William Tell Overture. The chicks are deep in some serious imaginative play. And it looks like this:
Do you know what this is? It's a monster being killed. I know it looks more like "pack the trunk of the car" or "let's pretend we're piling stuff up to donate to the Salvation Army" or "let's pretend we're masons and build a wall." And the truth is...if they were playing any of those things, it would still look like this. Play, for the chicks, involves an insane amount of moving stuff into different places, or filling up bags with stuff, covering the couch with stuff, etc.
And while I look at a freshly-cleaned living room and think "ahh...peace and tranquility," they look at it and and see a blank canvas just waiting to be altered. There's no moment more likely to lead to a long fit of messy imaginative play than the moment after I've finished cleaning.