I don't believe in it, imagine if you came back as a slug or something, you'd know that at some point you would either be trodden on or mutilated by a 5 year old!

Any with no limbs, you wouldn't be able to do yourself in!!!

Plus, if it is true, then would you move up or down in ranks of what you come back as depending on how you spend your life, and if so, if you don't know that you will be coming back then how can you know to better the efforts you made in the life you just had?