Ted, frailing is similar to up-picking: pick up on a string on one, brush down across all the strings with your fingernails on two, and play the fifth string with your thumb at "and" for a boom-tiddy, boom-tiddy rhythm. In frailing, you pick down with your fingernail on one, with the other parts of the stroke being the same as with up picking. The advantage is that in frailing, the action is initiated at the elbow and shoulder rather than at the finger so it is possible to generate a more driving rhythm.

In up-picking, double thumbing is accomplished by a pinching motion: pick up at one, thumb the 2nd, 3rd, or fourth string at and; strum at 2, thumb the fifth string at and: boomdy tiddy, boomdy tiddy. In frailing (double thumb frailing is called "clawhammer"), the thumb has to move into position on a string just as the fingernail hits a string, and the thumb pluck comes as you raise your hand for the brush (or another single string) stroke.

As for the reversed picks, your fingernails can be abraded away by hard frailing and many players use fingerpicks turned backwards: some metal picks are made especially light for frailers to use--and to match the volume of the frailed strings, many players also use thumb picks.

I hope my explanation makes sense. --seed