Here's how to achieve this look:
1) Paint a thickish base coat of OPI's Pamplona Purple on one nail.
2) Dab on some thick, random blobs of China Glaze's First Mate on the nail (while base coat is still wet).
3) Dab on some more random blobs of OPI's Ogre the Top.
4) Take a toothpick and start randomly swirling the paint together on the wet nail.
5) Top coat it!
Two key things:
1) "Random" is the word to live by with this. Don't try to be too uniform because it'll drive you crazy because it's nearly impossible to do.
2) If one color starts overtaking another, add another drop of whatever color is lacking while everything is wet.