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[Splitmore]

natpython,
Usually lethargy is the only sign of a sick snake and often by this stage it's too late to save the animal.I've had some of the healthiest looking pythons just head down hill and die within a week for no apparent reason. Even had autopsies done that really didn't show anything up.
The swelling and fluid coming from the mouth is just the snakes starting to decompose.If a snake dies on top of the heat source this can start to happen after only a few hours but usually takes a day or two to reach that stage.
Regards,
Splitmore