Genetics gone haywire.Not all that uncommon actually in any species.Hardly surprising in frogs though considering the amount of things going on when they're changing from tads to the full blown frog.
I have a pic of a 2 headed fish in one of my books somewhere.
omg,how adf eat their on legs??lol is weird to know about those kind of deformity.At my lfs i saw 1 3 tailed gold fish,and the price for it is freaking high,is about 60bucks for that gold fish which juz 2inch size.lol.