Could be that someone forgot to reset the igniter CBs after maintenance. Happened to me on a 1-11 once. I happened to be stood underneath it at the time holding the start valve open!!! The flight crew realised that the EGT wasn't moving, checked the CB panel and pushed them back in. WOOOOOOOOF!!!
Never moved so fast in my life.
Mind you considering that the 737 is being filmed suggests that they knew this was going to happen so ignore the above cobblers.
