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Alright, assuming for a moment that this is not a troll post, a snake upside-down and not righting itself is generally a sign of sickness, usually a neurological problem. A snake floating upside-down in water suggests to me that said snake drowned. If your snake IS alive, then I suggest you get some medical help to determine why it's doing this. My guess, if you do indeed have an upside-down floating snake and aren't just posting this because you think it's funny, is that he's dead.