Maybe.... it is suppossed to symbolise America being injured by 9/11 (as the dog has apparently been impaled by a US flag...really subtle there). Os it's saying that the terrorist attack has had the same effect as cutting of the hind leg of a dog - i.e. severely damaging and near crippling the country for all time (as a dogs leg won't grow back).
And it's standing on sticks, for lack of a better word, to illustrate how the US holds itself as being better than the rest of the world. Except a 3 legged dog probably wouldn't be able to balance on that sort of platform, so it'll soon fall down - maybe symobilising that the terrorists have succeeded in placing the US on the edge of a precipice (by removing the leg), and thus the US will collapse and destroy itself if it continues to hold itself on that pedestal (by losing balance) - so its only hope is to lower itself from it.
this, however, is truly bizarre;
Is it something to do with bombing farmers until their land collapses
low enough to flood?
