I guess you have to get creative to make a sack of flour burst like that without using any explosives, that would lead to a nasty dust explosion.
Flour Bombs are not creative. we tossed those around as kids a lot.
Then mom told us we wouldn't be having pancakes as we were out of flour.
We made crazy snot after that. (in case you want to know; the powdery laundry detergent and liquid dishwasher soup mixed together) Trust me that gave a major mess. :}
All she needs is a match.
Mind you, I wouldn't want to be in the same room when she lights it. Some of the biggest industrial explosions have taken place in flour mills over the years. And just ask any grain elevator about the lengths they go to to prevent any source of ignition taking place.