See them starting to gather? Looks like the evil twin of friendly sing and dance "flash mobs" has reared her ugly head.

In St. Paul, Minnesota on Saturday, a mob of 50 teenagers stormed a convenience store and "mob robbed" it.

We'd never heard of mob theft until today, but apparently it's what happens when a large number of people swarm a place and take everything in sight, and it's happened once before in St. Louis.

A policeman described what happens:

"They steal your basic convenience store type of goods and run out," says St. Paul Police Department spokesperson Andy Skoogman.

It sounds kind of like a relatively harmless version of some of the food riots happening around the world.

But what's disturbing is that it's the second "mob theft" incident in St. Paul in less than six months (the first one happened at a BP station), and apparently there have been incidents in other cities, so police are worried that it's a trend to watch out for.

UPDATE: Mob robbers have attacked in a Milwaukee/Wauwatosa, MN mall, too.

Click here to watch a video of what happened >