Did anybody else hear that when the entire explosion didn't happen at the hospital, and joker kept tapping on the detonator, that it was an actual malfunction and the scene was improvised? Apparently they actually blew up an old abandoned factory rather than use a lot of CGI or even a scaled down building, which doesn't lend itself well to retakes. Apparently there was a technical malfunction, and not all the explosives went off when they were supposed to, and Ledger improvised the Joker looking confused and repeatedly hitting the buttons until it blew up.