First domino is the UK. Johnson needs to do something about the underhand funding deal to prop up the Euro in case of financial calamity ASAP.
Second domino is Italy. Too many bad bank debts that can't be hived off and sold to unsuspecting dolts.
It's all fake paper. No actual gold has changed hands.
With paper, it's easy to sell short (i.e. dump something that you don't have) - this causes trips to fire on automated accounts, which sell at certain levels, thus starting a cascade. The original dumper then buys back at lower than they sold and pockets the difference.