This False cut has to be done in one smooth rythm. It's most deceptive when it's done on the off beat. Begin by swing cutting one third of the deck from the Right hand to the left hand (fig.1)
As soon as the packet of cards are in the left hand your left index finger curls under the packet. Notice how in figure 2 the packet is entirely hold by the index and middle finger. The thumb rests on top of the packet.
Now bend the index and middle finger of the left hand. The situation should be like in figure3. Study the photograph for details
Swing cut the second third part of the deck into the left hand, but let the cards between the index and middle finger steady. As you can see the left thumb holds the second (middle)part of the deck in position. See figure 4 for details
Close the index and middle finger of the left hand in the reverse fashion like in figure 3. This puts the top part on the middle part again. See figure 5.
Take the remainder of the deck in the right hand and bump it two or three times against the left hand packet. This is a misdirection used in several false cuts. It should look like you're straightening the right hand cards with the left hand packet. Figure 6 is a freeze of the action.
Finish by placing the right hand packet to the the table and put the left hand packet on top. Everything should be in same order as you started in the beginning.