This is a sign of the female being receptive to breeding.It is a pre-breeding part of the ritual. My animals that bred last year thrashed thier tails and moments later I caught 2 pairs locked-up. You may have hognose eggs this year. GOOD LUCK! :A couple of my female hog thrash there tails around when I put them in with a male hog ..does this mean there not ready to breed right now ..or is it nothing ??